// Copyright (C) 2016 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package gles

import (
	"bytes"
	"fmt"
	"reflect"

	"android.googlesource.com/platform/tools/gpu/framework/binary/cyclic"
	"android.googlesource.com/platform/tools/gpu/framework/binary/vle"
	"android.googlesource.com/platform/tools/gpu/framework/device"
	"android.googlesource.com/platform/tools/gpu/framework/interval"
	"android.googlesource.com/platform/tools/gpu/framework/log"
	"android.googlesource.com/platform/tools/gpu/framework/shadertools"
	"android.googlesource.com/platform/tools/gpu/gapid/atom"
	"android.googlesource.com/platform/tools/gpu/gapid/config"
	"android.googlesource.com/platform/tools/gpu/gapid/database"
	"android.googlesource.com/platform/tools/gpu/gapid/gfxapi"
	"android.googlesource.com/platform/tools/gpu/gapid/gfxapi/gles/glsl/ast"
	"android.googlesource.com/platform/tools/gpu/gapid/gfxapi/state"
	"android.googlesource.com/platform/tools/gpu/gapid/memory"
	"android.googlesource.com/platform/tools/gpu/gapid/replay"
	"android.googlesource.com/platform/tools/gpu/gapid/replay/builder"
)

type support int

const (
	unsupported support = iota
	supported
	required
)

var (
	// We don't include tests directly in the gles package as it adds
	// signaficantly to the test build time.
	VisibleForTestingCompat     = compat
	VisibleForTestingGlSlCompat = glslCompat
)

// If the default vertex array object (id 0) is not allowed on
// the target platform, we remap the uses to this array.
const DefaultVertexArrayId = VertexArrayId(0xFFFF0001)

type extensions map[string]struct{}

func listToExtensions(list []string) extensions {
	out := extensions{}
	for _, s := range list {
		out[s] = struct{}{}
	}
	return out
}

func translateExtensions(in U32ːstringᵐ) extensions {
	out := make(extensions, len(in))
	for _, s := range in {
		out[s] = struct{}{}
	}
	return out
}

func (e extensions) get(name string) support {
	if _, ok := e[name]; ok {
		return supported
	}
	return unsupported
}

func (s support) String() string {
	switch s {
	case unsupported:
		return "unsupported"
	case supported:
		return "supported"
	case required:
		return "required"
	default:
		return fmt.Sprintf("support<%d>", s)
	}
}

type features struct {
	vertexHalfFloatOES        support // support for GL_OES_vertex_half_float
	eglImageExternal          support // support for GL_OES_EGL_image_external
	vertexArrayObjects        support // support for VBOs
	supportGenerateMipmapHint bool    // support for GL_GENERATE_MIPMAP_HINT
	compressedTextureFormats  map[GLenum]struct{}
	framebufferSrgb           support // support for GL_FRAMEBUFFER_SRGB
}

func getFeatures(ctx log.Context, version string, ext extensions) (features, *Version, error) {
	v, err := ParseVersion(version)
	if err != nil {
		return features{}, v, err
	}

	f := features{
		vertexHalfFloatOES:        ext.get("GL_OES_vertex_half_float"),
		eglImageExternal:          ext.get("GL_OES_EGL_image_external"),
		compressedTextureFormats:  getSupportedCompressedTextureFormats(ext),
		supportGenerateMipmapHint: v.IsES,
	}

	// TODO: Properly check the specifications for these flags.
	switch {
	case v.IsES && v.Major >= 3:
		f.vertexArrayObjects = supported
	case !v.IsES && v.Major >= 3:
		f.vertexArrayObjects = required
	}

	// GLES defaults FRAMEBUFFER_SRGB to enabled and only allows changing it via
	// an extension, while desktop GL defaults to disabled.
	if v.IsES {
		f.framebufferSrgb = ext.get("GL_EXT_sRGB_write_control")
	} else {
		f.framebufferSrgb = required
	}

	return f, v, nil
}

type scratchBuffer struct {
	size GLsizeiptr
	id   BufferId
}

func cloneAtom(a atom.Atom) atom.Atom {
	var b bytes.Buffer
	cyclic.Encoder(vle.Writer(&b)).Variant(a)
	return (cyclic.Decoder(vle.Reader(&b)).Variant()).(atom.Atom)
}

func compat(ctx log.Context, device *device.Information, d database.Database) (atom.Transformer, error) {
	ctx = ctx.Enter("compat")

	glDev := device.Configuration.GraphicsDrivers.OpenGL
	target, version, err := getFeatures(ctx, glDev.Version, listToExtensions(glDev.Extensions))
	if err != nil {
		return nil, fmt.Errorf(
			"Error '%v' when getting feature list for version: '%s', extensions: '%s'.",
			err, glDev.Version, glDev.Extensions)
	}

	contexts := map[*Context]features{}

	s := state.New(ctx)

	scratchBuffers := map[interface{}]scratchBuffer{}
	nextBufferID := BufferId(0xffff0000)
	newBuffer := func(out atom.Writer) BufferId {
		id := nextBufferID
		tmp := atom.Must(atom.AllocData(ctx, s, d, id))
		out.Write(ctx, atom.NoID, NewGlGenBuffers(1, tmp.Ptr()).AddWrite(tmp.Data()))
		nextBufferID--
		return id
	}

	textureCompat := &textureCompat{
		f:                    target,
		v:                    version,
		ctx:                  ctx,
		s:                    s,
		d:                    d,
		textureCompatSwizzle: map[*Texture]map[GLenum]GLenum{},
	}

	var t atom.Transformer
	t = atom.Transform("compat", func(ctx log.Context, i atom.ID, a atom.Atom, out atom.Writer) {
		switch a := a.(type) {
		case *EglMakeCurrent: // TODO: Check for GLX, CGL, WGL...
			// The compatibility layer introduces calls to GL functions that are defined for desktop GL
			// and for GLES 3.0+. If the trace originated on a GLES 2.0 device, these new atoms' mutate
			// functions will fail the minRequiredVersion checks (which look at the version coming from
			// the original context from the trace).
			// TODO(dsrbecky): This might make some atoms valid for replay which were invalid on trace.
			scs := FindStaticContextState(a.Extras())
			if scs != nil && !version.IsES && scs.Constants.MajorVersion < 3 {
				a = cloneAtom(a).(*EglMakeCurrent)
				scs = FindStaticContextState(a.Extras())
				scs.Constants.MajorVersion = 3
				scs.Constants.MinorVersion = 0
			}

			// Mutate to set the context, Version and Extensions strings.
			mutateAndWrite(ctx, i, a, s, d, out)

			c := GetContext(s)
			if c == nil || !c.Info.Initialized {
				return
			}
			if _, found := contexts[c]; found {
				return
			}

			source, _, err := getFeatures(ctx, c.Constants.Version, translateExtensions(c.Constants.Extensions))
			if err != nil {
				ctx.Error().V("version", c.Constants.Version).V("extensions", c.Constants.Extensions).
					Fail(err, "Getting feature list.")
				return
			}

			contexts[c] = source

			if target.vertexArrayObjects == required &&
				source.vertexArrayObjects != required {
				// Replay device requires VAO, but capture did not enforce it.
				// Satisfy the target by creating and binding a single VAO
				// which we will use instead of the default VAO (id 0).
				tmp := atom.Must(atom.AllocData(ctx, s, d, VertexArrayId(DefaultVertexArrayId)))
				out.Write(ctx, atom.NoID, NewGlGenVertexArrays(1, tmp.Ptr()).AddWrite(tmp.Data()))
				out.Write(ctx, atom.NoID, NewGlBindVertexArray(DefaultVertexArrayId))
			}
			return
		}

		c := GetContext(s)
		if c == nil {
			// The compatibility translations below assume that we have a valid context.
			mutateAndWrite(ctx, i, a, s, d, out)
			return
		}

		switch a := a.(type) {
		case *GlBindBuffer:
			if a.Buffer != 0 && !c.Instances.Buffers.Contains(a.Buffer) {
				// glGenBuffers() was not used to generate the buffer. Legal in GLES 2.
				tmp := atom.Must(atom.AllocData(ctx, s, d, a.Buffer))
				out.Write(ctx, atom.NoID, NewGlGenBuffers(1, tmp.Ptr()).AddRead(tmp.Data()))
			}

		case *GlBindTexture:
			if !c.Instances.Textures.Contains(a.Texture) {
				// glGenTextures() was not used to generate the texture. Legal in GLES 2.
				tmp := atom.Must(atom.AllocData(ctx, s, d, VertexArrayId(a.Texture)))
				out.Write(ctx, atom.NoID, NewGlGenTextures(1, tmp.Ptr()).AddRead(tmp.Data()))
			}

			if a.Target == GLenum_GL_TEXTURE_EXTERNAL_OES && target.eglImageExternal == unsupported {
				// TODO: Implement full support for external images.
				// Remap external textures to plain 2D textures - this matches GLSL compat.
				out.Write(ctx, atom.NoID, NewGlBindTexture(GLenum_GL_TEXTURE_2D, a.Texture))
				return
			}

		case *GlBindVertexArray:
			if a.Array == VertexArrayId(0) {
				if target.vertexArrayObjects == required &&
					contexts[c].vertexArrayObjects != required {
					a.Mutate(ctx, s, d, nil /* no builder, just mutate */)
					out.Write(ctx, atom.NoID, NewGlBindVertexArray(DefaultVertexArrayId))
					return
				}
			}

		case *GlBindVertexArrayOES:
			if a.Array == VertexArrayId(0) {
				if target.vertexArrayObjects == required &&
					contexts[c].vertexArrayObjects != required {
					a.Mutate(ctx, s, d, nil /* no builder, just mutate */)
					out.Write(ctx, atom.NoID, NewGlBindVertexArray(DefaultVertexArrayId))
					return
				}
			}

		case *GlBindBufferRange:
			misalignment := a.Offset % GLintptr(glDev.UniformBufferAlignment)
			if a.Target == GLenum_GL_UNIFORM_BUFFER && misalignment != 0 {
				// We have a glBindBufferRange() taking a uniform buffer with an
				// illegal offset alignment.
				// TODO: We don't handle the case where the buffer is kept bound
				// while the buffer is updated. It's an unlikely issue, but
				// something that may break us.
				if _, ok := c.Instances.Buffers[a.Buffer]; !ok {
					return // Don't know what buffer this is referring to.
				}

				// We need a scratch buffer to copy the buffer data to a correct
				// alignment.
				key := struct {
					c      *Context
					Target GLenum
					Index  GLuint
				}{c, a.Target, a.Index}

				// Look for pre-existing buffer we can reuse.
				buffer, ok := scratchBuffers[key]
				if !ok {
					buffer.id = newBuffer(out)
					scratchBuffers[key] = buffer
				}

				// Bind the scratch buffer to GL_COPY_WRITE_BUFFER
				out.Write(ctx, atom.NoID, NewGlBindBuffer(GLenum_GL_COPY_WRITE_BUFFER, buffer.id))

				if buffer.size < a.Size {
					// Resize the scratch buffer
					out.Write(ctx, atom.NoID, NewGlBufferData(GLenum_GL_COPY_WRITE_BUFFER, a.Size, memory.Nullptr, GLenum_GL_DYNAMIC_COPY))
					buffer.size = a.Size
					scratchBuffers[key] = buffer
				}

				// Copy out the misaligned data to the scratch buffer in the
				// GL_COPY_WRITE_BUFFER binding.
				out.Write(ctx, atom.NoID, NewGlBindBuffer(a.Target, a.Buffer))
				out.Write(ctx, atom.NoID, NewGlCopyBufferSubData(a.Target, GLenum_GL_COPY_WRITE_BUFFER, a.Offset, 0, a.Size))

				// We can now bind the range with correct alignment.
				out.Write(ctx, i, NewGlBindBufferRange(a.Target, a.Index, buffer.id, 0, a.Size))

				// Restore old GL_COPY_WRITE_BUFFER binding.
				out.Write(ctx, atom.NoID, NewGlBindBuffer(GLenum_GL_COPY_WRITE_BUFFER, c.BoundBuffers.CopyWriteBuffer))

				return
			}

		case *GlDisableVertexAttribArray:
			vao := c.Instances.VertexArrays[c.BoundVertexArray]
			if vao.VertexAttributeArrays[a.Location].Enabled == GLboolean_GL_FALSE {
				// Ignore the call if it is redundant (i.e. it is already disabled).
				// Some applications iterate over all arrays and explicitly disable them.
				// This is a problem if the target supports fewer arrays than the capture.
				return
			}

		case *GlVertexAttrib4fv:
			if oldAttrib, ok := c.VertexAttributes[a.Location]; ok {
				oldValue := oldAttrib.Value.Read(ctx, a, s, d, nil /* builder */)
				a.Mutate(ctx, s, d, nil /* no builder, just mutate */)
				newAttrib := c.VertexAttributes[a.Location]
				newValue := newAttrib.Value.Read(ctx, a, s, d, nil /* builder */)
				if reflect.DeepEqual(oldValue, newValue) {
					// Ignore the call if it is redundant.
					// Some applications iterate over all arrays and explicitly initialize them.
					// This is a problem if the target supports fewer arrays than the capture.
					return
				}
			}
			out.Write(ctx, i, a)
			return

		case *GlGetVertexAttribIiv,
			*GlGetVertexAttribIuiv,
			*GlGetVertexAttribPointerv,
			*GlGetVertexAttribfv,
			*GlGetVertexAttribiv:
			// Some applications iterate over all arrays and query their state.
			// This may fail if the target supports fewer arrays than the capture.
			// As these should have no side-effects, just drop them.
			return

		case *GlShaderSource:
			// Apply the state mutation of the unmodified glShaderSource atom.
			// This is so we can grab the source string from the Shader object.
			if err := a.Mutate(ctx, s, d, nil /* no builder, just mutate */); err != nil {
				return
			}
			shader := c.Instances.Shaders.Get(a.Shader)
			src := ""

			if config.UseGlslang {
				opts := shadertools.Option{
					IsFragmentShader: shader.Type == GLenum_GL_FRAGMENT_SHADER,
					IsVertexShader:   shader.Type == GLenum_GL_VERTEX_SHADER,
				}

				res := shadertools.ConvertGlsl(shader.Source, &opts)
				if !res.Ok {
					ctx.Error().V("id", i).Logf("Failed to translate GLSL:\n%s\nSource:%s\n", res.Message, shader.Source)
					return
				}
				src = res.SourceCode
			} else {
				lang := ast.LangVertexShader
				switch shader.Type {
				case GLenum_GL_VERTEX_SHADER:
				case GLenum_GL_FRAGMENT_SHADER:
					lang = ast.LangFragmentShader
				default:
					ctx.Warning().V("type", shader.Type).Log("Unknown shader type")
				}

				src, err = glslCompat(ctx, shader.Source, lang, device, d)
				if err != nil {
					ctx.Error().V("id", i).Fail(err, "Reformatting GLSL source for atom")
				}
			}

			tmpSrc := atom.Must(atom.AllocData(ctx, s, d, src))
			tmpPtrToSrc := atom.Must(atom.AllocData(ctx, s, d, tmpSrc.Ptr()))
			a = NewGlShaderSource(a.Shader, 1, tmpPtrToSrc.Ptr(), memory.Nullptr).
				AddRead(tmpSrc.Data()).
				AddRead(tmpPtrToSrc.Data())
			mutateAndWrite(ctx, i, a, s, d, out)
			return

		// TODO: glVertexAttribIPointer
		case *GlVertexAttribPointer:
			if a.Type == GLenum_GL_HALF_FLOAT_OES && target.vertexHalfFloatOES == unsupported {
				// Convert GL_HALF_FLOAT_OES to GL_HALF_FLOAT_ARB.
				a = NewGlVertexAttribPointer(a.Location, a.Size, GLenum_GL_HALF_FLOAT_ARB, a.Normalized, a.Stride, memory.Pointer(a.Data))
			}
			if target.vertexArrayObjects == required &&
				c.BoundBuffers.ArrayBuffer == 0 {
				// Client-pointers are not supported, we need to copy this data to a buffer.
				// However, we can't do this now as the observation only happens at the draw call.
				// Apply the state changes, but don't write the emit the atom - we need to defer
				// the trickery to the draw call.
				a.Mutate(ctx, s, d, nil /* no builder, just mutate */)
				return
			}
			mutateAndWrite(ctx, i, a, s, d, out)
			return

		case *GlDrawArrays:
			if target.vertexArrayObjects == required {
				if clientVAsBound(c) {
					first := int(a.FirstIndex)
					last := first + int(a.IndicesCount) - 1
					defer moveClientVBsToVAs(ctx, first, last, i, a, s, c, d, out)()
				}
			}

		case *GlDrawElements:
			if target.vertexArrayObjects == required {
				e := externs{ctx: ctx, a: a, s: s, d: d}

				ib := c.Instances.VertexArrays[c.BoundVertexArray].ElementArrayBuffer
				clientIB := ib == 0
				clientVB := clientVAsBound(c)
				if clientIB {
					// The indices for the glDrawElements call is in client memory.
					// We need to move this into a temporary buffer.

					// Generate a new element array buffer and bind it.
					id := BufferId(newUnusedID(func(x uint32) bool { _, ok := c.Instances.Buffers[BufferId(x)]; return ok }))
					c.Instances.Buffers[id] = &Buffer{} // Not used aside from reserving the ID.
					tmp := atom.Must(atom.AllocData(ctx, s, d, id))
					out.Write(ctx, atom.NoID, NewGlGenBuffers(1, tmp.Ptr()).AddRead(tmp.Data()))
					out.Write(ctx, atom.NoID, NewGlBindBuffer(GLenum_GL_ELEMENT_ARRAY_BUFFER, id))

					// By moving the draw call's observations earlier, populate the element array buffer.
					size, base := DataTypeSize(a.IndicesType)*int(a.IndicesCount), memory.Pointer(a.Indices)
					glBufferData := NewGlBufferData(GLenum_GL_ELEMENT_ARRAY_BUFFER, GLsizeiptr(size), memory.Pointer(base), GLenum_GL_STATIC_DRAW)
					glBufferData.extras = a.extras
					out.Write(ctx, atom.NoID, glBufferData)

					// Clean-up
					defer func() {
						out.Write(ctx, atom.NoID, NewGlBindBuffer(GLenum_GL_ELEMENT_ARRAY_BUFFER, ib))
						delete(c.Instances.Buffers, id)
					}()

					if clientVB {
						// Some of the vertex arrays for the glDrawElements call is in
						// client memory and we need to move this into temporary buffer(s).
						// The indices are also in client memory, so we need to apply the
						// atom's reads now so that the indices can be read from the
						// application pool.
						a.Extras().Observations().ApplyReads(s.Memory[memory.ApplicationPool])
						limits := e.calcIndexLimits(U8ᵖ(a.Indices), a.IndicesType, 0, uint32(a.IndicesCount))
						defer moveClientVBsToVAs(ctx, int(limits.Min), int(limits.Max), i, a, s, c, d, out)()
					}

					glDrawElements := *a
					glDrawElements.Indices.Address = 0
					glDrawElements.Mutate(ctx, s, d, nil /* no builder, just mutate */)
					out.Write(ctx, i, &glDrawElements)
					return

				} else if clientVB { // GL_ELEMENT_ARRAY_BUFFER is bound
					// Some of the vertex arrays for the glDrawElements call is in
					// client memory and we need to move this into temporary buffer(s).
					// The indices are server-side, so can just be read from the internal
					// pooled buffer.
					data := c.Instances.Buffers[ib].Data.Index(0, s)
					base := uint32(a.Indices.Address)
					limits := e.calcIndexLimits(data, a.IndicesType, base, uint32(a.IndicesCount))
					defer moveClientVBsToVAs(ctx, int(limits.Min), int(limits.Max), i, a, s, c, d, out)()
				}
			}

		case *GlCompressedTexImage2D:
			if _, supported := target.compressedTextureFormats[a.Format]; !supported {
				if err := decompressTexImage2D(ctx, i, a, s, d, out); err == nil {
					return
				}
				ctx.Fail(err, "Decompressing texture")
			}

		case *GlCompressedTexSubImage2D:
			if _, supported := target.compressedTextureFormats[a.Format]; !supported {
				if err := decompressTexSubImage2D(ctx, i, a, s, d, out); err == nil {
					return
				}
				ctx.Fail(err, "Decompressing texture")
			}

		// TODO: glTexStorage functions are not guaranteed to be supported. Consider replacing with glTexImage calls.
		// TODO: Handle glTextureStorage family of functions - those use direct state access, not the bound texture.
		case *GlTexStorage1DEXT:
			{
				a := *a
				textureCompat.convertFormat(a.Target, &a.Internalformat, nil, nil, out)
				if !version.IsES { // Strip suffix on desktop.
					a := NewGlTexStorage1D(a.Target, a.Levels, a.Internalformat, a.Width)
					mutateAndWrite(ctx, i, a, s, d, out)
					return
				}
				mutateAndWrite(ctx, i, &a, s, d, out)
				return
			}
		case *GlTexStorage2D:
			{
				a := *a
				textureCompat.convertFormat(a.Target, &a.Internalformat, nil, nil, out)
				mutateAndWrite(ctx, i, &a, s, d, out)
				return
			}
		case *GlTexStorage2DEXT:
			{
				a := *a
				textureCompat.convertFormat(a.Target, &a.Internalformat, nil, nil, out)
				if !version.IsES { // Strip suffix on desktop.
					a := NewGlTexStorage2D(a.Target, a.Levels, a.Internalformat, a.Width, a.Height)
					mutateAndWrite(ctx, i, a, s, d, out)
					return
				}
				mutateAndWrite(ctx, i, &a, s, d, out)
				return
			}
		case *GlTexStorage2DMultisample:
			{
				a := *a
				textureCompat.convertFormat(a.Target, &a.Internalformat, nil, nil, out)
				mutateAndWrite(ctx, i, &a, s, d, out)
				return
			}
		case *GlTexStorage3D:
			{
				a := *a
				textureCompat.convertFormat(a.Target, &a.Internalformat, nil, nil, out)
				mutateAndWrite(ctx, i, &a, s, d, out)
				return
			}
		case *GlTexStorage3DEXT:
			{
				a := *a
				textureCompat.convertFormat(a.Target, &a.Internalformat, nil, nil, out)
				if !version.IsES { // Strip suffix on desktop.
					a := NewGlTexStorage3D(a.Target, a.Levels, a.Internalformat, a.Width, a.Height, a.Depth)
					mutateAndWrite(ctx, i, a, s, d, out)
					return
				}
				mutateAndWrite(ctx, i, &a, s, d, out)
				return
			}
		case *GlTexStorage3DMultisample:
			{
				a := *a
				textureCompat.convertFormat(a.Target, &a.Internalformat, nil, nil, out)
				mutateAndWrite(ctx, i, &a, s, d, out)
				return
			}
		case *GlTexStorage3DMultisampleOES:
			{
				a := *a
				textureCompat.convertFormat(a.Target, &a.Internalformat, nil, nil, out)
				if !version.IsES { // Strip suffix on desktop.
					a := NewGlTexStorage3DMultisample(a.Target, a.Samples, a.Internalformat, a.Width, a.Height, a.Depth, a.Fixedsamplelocations)
					mutateAndWrite(ctx, i, a, s, d, out)
					return
				}
				mutateAndWrite(ctx, i, &a, s, d, out)
				return
			}
		case *GlTexImage2D:
			{
				a := *a
				internalformat := GLenum(a.Internalformat)
				textureCompat.convertFormat(a.Target, &internalformat, &a.Format, &a.Type, out)
				a.Internalformat = GLint(internalformat)
				mutateAndWrite(ctx, i, &a, s, d, out)
				return
			}
		case *GlTexImage3D:
			{
				a := *a
				internalformat := GLenum(a.Internalformat)
				textureCompat.convertFormat(a.Target, &internalformat, &a.Format, &a.Type, out)
				a.Internalformat = GLint(internalformat)
				mutateAndWrite(ctx, i, &a, s, d, out)
				return
			}
		case *GlTexImage3DOES:
			{
				a := *a
				textureCompat.convertFormat(a.Target, &a.Internalformat, &a.Format, &a.Type, out)
				if !version.IsES { // Strip suffix on desktop.
					extras := a.extras
					a := NewGlTexImage3D(a.Target, a.Level, GLint(a.Internalformat), a.Width, a.Height, a.Depth, a.Border, a.Format, a.Type, memory.Pointer(a.Pixels))
					a.extras = extras
					mutateAndWrite(ctx, i, a, s, d, out)
					return
				}
				mutateAndWrite(ctx, i, &a, s, d, out)
				return
			}
		case *GlTexSubImage2D:
			{
				a := *a
				textureCompat.convertFormat(a.Target, nil, &a.Format, &a.Type, out)
				mutateAndWrite(ctx, i, &a, s, d, out)
				return
			}
		case *GlTexSubImage3D:
			{
				a := *a
				textureCompat.convertFormat(a.Target, nil, &a.Format, &a.Type, out)
				mutateAndWrite(ctx, i, &a, s, d, out)
				return
			}
		case *GlTexSubImage3DOES:
			{
				a := *a
				textureCompat.convertFormat(a.Target, nil, &a.Format, &a.Type, out)
				if !version.IsES { // Strip suffix on desktop.
					extras := a.extras
					a := NewGlTexSubImage3D(a.Target, a.Level, a.Xoffset, a.Yoffset, a.Zoffset, a.Width, a.Height, a.Depth, a.Format, a.Type, memory.Pointer(a.Pixels))
					a.extras = extras
					mutateAndWrite(ctx, i, a, s, d, out)
					return
				}
				mutateAndWrite(ctx, i, &a, s, d, out)
				return
			}
		case *GlCopyTexImage2D:
			{
				a := *a
				textureCompat.convertFormat(a.Target, &a.Internalformat, nil, nil, out)
				mutateAndWrite(ctx, i, &a, s, d, out)
				return
			}

		case *GlTexParameterIivOES:
			mutateAndWrite(ctx, i, a, s, d, out)
			textureCompat.postTexParameter(a.Target, a.Pname, out)
			return
		case *GlTexParameterIuivOES:
			mutateAndWrite(ctx, i, a, s, d, out)
			textureCompat.postTexParameter(a.Target, a.Pname, out)
			return
		case *GlTexParameterIiv:
			mutateAndWrite(ctx, i, a, s, d, out)
			textureCompat.postTexParameter(a.Target, a.Pname, out)
			return
		case *GlTexParameterIuiv:
			mutateAndWrite(ctx, i, a, s, d, out)
			textureCompat.postTexParameter(a.Target, a.Pname, out)
			return
		case *GlTexParameterf:
			mutateAndWrite(ctx, i, a, s, d, out)
			textureCompat.postTexParameter(a.Target, a.Parameter, out)
			return
		case *GlTexParameterfv:
			mutateAndWrite(ctx, i, a, s, d, out)
			textureCompat.postTexParameter(a.Target, a.Pname, out)
			return
		case *GlTexParameteri:
			mutateAndWrite(ctx, i, a, s, d, out)
			textureCompat.postTexParameter(a.Target, a.Parameter, out)
			return
		case *GlTexParameteriv:
			mutateAndWrite(ctx, i, a, s, d, out)
			textureCompat.postTexParameter(a.Target, a.Pname, out)
			return
		case *GlTexParameterIivEXT:
			mutateAndWrite(ctx, i, a, s, d, out)
			textureCompat.postTexParameter(a.Target, a.Pname, out)
			return
		case *GlTexParameterIuivEXT:
			mutateAndWrite(ctx, i, a, s, d, out)
			textureCompat.postTexParameter(a.Target, a.Pname, out)
			return

		case *GlProgramBinary:
			if !canUsePrecompiledShader(c, glDev) {
				for _, a := range buildStubProgram(ctx, a.Extras(), s, d, a.Program) {
					mutateAndWrite(ctx, atom.NoID, a, s, d, atom.TransformWriter{T: t, O: out})
				}
				return
			}

		case *GlProgramBinaryOES:
			if !canUsePrecompiledShader(c, glDev) {
				for _, a := range buildStubProgram(ctx, a.Extras(), s, d, a.Program) {
					mutateAndWrite(ctx, atom.NoID, a, s, d, atom.TransformWriter{T: t, O: out})
				}
				return
			}

		case *GlHint:
			if a.Target == GLenum_GL_GENERATE_MIPMAP_HINT && !target.supportGenerateMipmapHint {
				return // Not supported in the core profile of OpenGL.
			}

		case *GlGetBooleani_v,
			*GlGetBooleanv,
			*GlGetFloatv,
			*GlGetInteger64i_v,
			*GlGetInteger64v,
			*GlGetIntegeri_v,
			*GlGetIntegerv,
			*GlGetInternalformativ,
			*GlGetString,
			*GlGetStringi:
			// The acceptable values of these get functions vary between GL versions.
			// As these should have no side-effects, just drop them.
			return

		case *GlGetActiveAttrib,
			*GlGetActiveUniform:
			// The number of active attributes and uniforms can vary between compilers
			// depending on their ability to eliminate dead code. In particular,
			// dead code in pixel shader can allow code removal in the vertex shader.
			// As these should have no side-effects, just drop them.
			return

		case *GlLabelObjectEXT,
			*GlGetObjectLabelEXT,
			*GlObjectLabel,
			*GlObjectLabelKHR,
			*GlGetObjectLabel,
			*GlObjectPtrLabel,
			*GlGetObjectPtrLabel,
			*GlGetObjectLabelKHR:
			// These methods require non-trivial remapping for replay.
			// As they do not affect rendering output, just drop them.
			return

		case *GlInsertEventMarkerEXT,
			*GlPushGroupMarkerEXT,
			*GlPopGroupMarkerEXT:
			// GL_EXT_debug_marker may not be supported on the replay device.
			// As they do not affect rendering output, just drop them.
			return

		case *GlGetProgramBinary,
			*GlGetProgramBinaryOES:
			// Program binaries are very driver specific. This command may fail on replay
			// because one of the arguments must be GL_PROGRAM_BINARY_LENGTH.
			// It has no side effects, so just drop it.
			return

		case *GlEnable:
			if a.Capability == GLenum_GL_FRAMEBUFFER_SRGB &&
				target.framebufferSrgb == required && contexts[c].framebufferSrgb != required &&
				c.BoundFramebuffers[GLenum_GL_DRAW_FRAMEBUFFER] == 0 {
				// Ignore enabling of FRAMEBUFFER_SRGB if the capture device did not
				// support an SRGB default framebuffer, but the replay device does. This
				// is only done if the current bound draw framebuffer is the default
				// framebuffer. The state is mutated so that when a non-default
				// framebuffer is bound later on, FRAMEBUFFER_SRGB will be enabled.
				// (see GlBindFramebuffer below)
				a.Mutate(ctx, s, d, nil /* no builder, just mutate */)
				return
			}

		case *GlDisable:
			// GL_QCOM_alpha_test adds back GL_ALPHA_TEST from GLES 1.0 as extension.
			// It seems that applications only disable it to make sure it is off, so
			// we can safely ignore it. We should not ignore glEnable for it though.
			if a.Capability == GLenum_GL_ALPHA_TEST_QCOM {
				return
			}

		case *GlGetGraphicsResetStatusEXT:
			// From extension GL_EXT_robustness
			// It may not be implemented by the replay driver.
			// It has no effect on rendering so just drop it.
			return

		case *GlInvalidateFramebuffer,
			*GlDiscardFramebufferEXT: // GL_EXT_discard_framebuffer
			// It may not be implemented by the replay driver.
			// It is only a hint so we can just drop it.
			// TODO: It has performance impact so we should not ignore it when profiling.
			return

		case *GlMapBufferOES:
			if !version.IsES { // Remove extension suffix on desktop.
				a := NewGlMapBuffer(a.Target, a.Access, memory.Pointer(a.Result))
				mutateAndWrite(ctx, i, a, s, d, out)
				return
			}

		case *GlMapBufferRangeEXT:
			if !version.IsES { // Remove extension suffix on desktop.
				a := NewGlMapBufferRange(a.Target, a.Offset, a.Length, a.Access, memory.Pointer(a.Result))
				mutateAndWrite(ctx, i, a, s, d, out)
				return
			}

		case *GlFlushMappedBufferRangeEXT:
			if !version.IsES { // Remove extension suffix on desktop.
				extras := a.extras
				a := NewGlFlushMappedBufferRange(a.Target, a.Offset, a.Length)
				a.extras = extras
				mutateAndWrite(ctx, i, a, s, d, out)
				return
			}

		case *GlUnmapBufferOES:
			if !version.IsES { // Remove extension suffix on desktop.
				extras := a.extras
				a := NewGlUnmapBuffer(a.Target, a.Result)
				a.extras = extras
				mutateAndWrite(ctx, i, a, s, d, out)
				return
			}

		case *GlBindFramebuffer:
			if target.framebufferSrgb == required && contexts[c].framebufferSrgb != required &&
				c.FragmentOperations.FramebufferSrgb != 0 {
				// Replay device defaults FRAMEBUFFER_SRGB to disabled and allows
				// enabling it (desktop), while the capture device defaulted to enabled
				// and may or may not have allowed it to be changed (GLES). While at the
				// same time, we currently assume that the default frame buffer is not
				// SRGB capable. Thus, when SRGB is enabled in the state, and we're
				// binding the default framebuffer, SRGB needs to be disabled, and
				// specifically enabled when binding the non-default framebuffer.
				// (If it was explicetly disabled in the capture, no change is needed.)
				// TODO: Handle the use of the EGL KHR_gl_colorspace extension.
				if a.Target == GLenum_GL_FRAMEBUFFER || a.Target == GLenum_GL_DRAW_FRAMEBUFFER {
					if a.Framebuffer == 0 {
						out.Write(ctx, atom.NoID, NewGlDisable(GLenum_GL_FRAMEBUFFER_SRGB))
					} else {
						out.Write(ctx, atom.NoID, NewGlEnable(GLenum_GL_FRAMEBUFFER_SRGB))
					}
				}
			}

		default:
			if a.AtomFlags().IsDrawCall() && clientVAsBound(c) {
				ctx.Warning().T("atom", a).Log("Draw call with client-pointers not handled by the compatability layer")
			}
		}

		mutateAndWrite(ctx, i, a, s, d, out)
	})

	return t, nil
}

func mutateAndWrite(ctx log.Context, i atom.ID, a atom.Atom, s *gfxapi.State, d database.Database, out atom.Writer) {
	a.Mutate(ctx, s, d, nil /* no builder, just mutate */)
	out.Write(ctx, i, a)
}

// canUsePrecompiledShader returns true if precompiled shaders / programs
// captured with the context c can be replayed on the device d.
func canUsePrecompiledShader(c *Context, d *device.OpenGLDriver) bool {
	return c.Constants.Vendor == d.Vendor && c.Constants.Version == d.Version
}

// clientVAsBound returns true if there are any vertex attribute arrays enabled
// with pointers to client-side memory.
func clientVAsBound(c *Context) bool {
	// Only the default vertex array can use client-side memory.
	if c.BoundVertexArray == 0 {
		va := c.Instances.VertexArrays[c.BoundVertexArray]
		for _, arr := range va.VertexAttributeArrays {
			if arr.Enabled == GLboolean_GL_TRUE {
				vb := va.VertexBufferBindings[arr.Binding]
				if vb.Buffer == 0 && arr.Pointer.Address != 0 {
					return true
				}
			}
		}
	}
	return false
}

// moveClientVBsToVAs is a compatability helper for transforming client-side
// vertex array data (which is not supported by glVertexAttribPointer in later
// versions of GL), into array-buffers.
func moveClientVBsToVAs(
	ctx log.Context,
	first, last int, // vertex indices
	i atom.ID,
	a atom.Atom,
	s *gfxapi.State,
	c *Context,
	d database.Database,
	out atom.Writer) (revert func()) {

	rngs := interval.U64RangeList{}
	// Gather together all the client-buffers in use by the vertex-attribs.
	// Merge together all the memory intervals that these use.
	va := c.Instances.VertexArrays[c.BoundVertexArray]
	for _, arr := range va.VertexAttributeArrays {
		if arr.Enabled == GLboolean_GL_TRUE {
			vb := va.VertexBufferBindings[arr.Binding]
			if vb.Buffer == 0 && arr.Pointer.Address != 0 {
				// TODO: We're currently ignoring the Offset and Stride fields of the VBB.
				// TODO: We're currently ignoring the RelativeOffset field of the VA.
				// TODO: Merge logic with ReadVertexArrays macro in vertex_arrays.api.
				if vb.Divisor != 0 {
					panic("Instanced draw calls not currently supported by the compatibility layer")
				}
				size := DataTypeSize(arr.Type) * int(arr.Size)
				stride := int(vb.Stride)
				base := memory.Pointer(arr.Pointer) // Always start from the 0'th vertex to simplify logic.
				rng := base.Range(uint64(last*stride + size))
				interval.Merge(&rngs, rng.Span(), true)
			}
		}
	}

	if len(rngs) == 0 {
		// Draw call does not use client-side buffers. Just draw.
		mutateAndWrite(ctx, i, a, s, d, out)
		return
	}

	// Create an array-buffer for each chunk of overlapping client-side buffers in
	// use. These are populated with data below.
	ids := make([]BufferId, len(rngs))
	for i := range rngs {
		id := BufferId(newUnusedID(func(x uint32) bool { _, ok := c.Instances.Buffers[BufferId(x)]; return ok }))
		c.Instances.Buffers[id] = &Buffer{} // Not used aside from reserving the ID.
		ids[i] = id
	}
	tmp := atom.Must(atom.AllocData(ctx, s, d, ids))
	out.Write(ctx, atom.NoID, NewGlGenBuffers(GLsizei(len(ids)), tmp.Ptr()).AddRead(tmp.Data()))

	// Apply the memory observations that were made by the draw call now.
	// We need to do this as the glBufferData calls below will require the data.
	out.Write(ctx, atom.NoID, replay.Custom(func(ctx log.Context, s *gfxapi.State, d database.Database, b *builder.Builder) error {
		a.Extras().Observations().ApplyReads(s.Memory[memory.ApplicationPool])
		return nil
	}))

	// Note: be careful of overwriting the observations made above, before the
	// calls to glBufferData below.

	// Fill the array-buffers with the observed memory data.
	for i, rng := range rngs {
		base := memory.Pointer{Address: rng.First, Pool: memory.ApplicationPool}
		size := GLsizeiptr(rng.Count)
		out.Write(ctx, atom.NoID, NewGlBindBuffer(GLenum_GL_ARRAY_BUFFER, ids[i]))
		out.Write(ctx, atom.NoID, NewGlBufferData(GLenum_GL_ARRAY_BUFFER, size, base, GLenum_GL_STATIC_DRAW))
	}

	// Redirect all the vertex attrib arrays to point to the array-buffer data.
	for l, arr := range va.VertexAttributeArrays {
		if arr.Enabled == GLboolean_GL_TRUE {
			vb := va.VertexBufferBindings[arr.Binding]
			if vb.Buffer == 0 && arr.Pointer.Address != 0 {
				i := interval.IndexOf(&rngs, arr.Pointer.Address)
				offset := arr.Pointer.Address - rngs[i].First
				out.Write(ctx, atom.NoID, NewGlBindBuffer(GLenum_GL_ARRAY_BUFFER, ids[i]))
				out.Write(ctx, atom.NoID, &GlVertexAttribPointer{
					Location:   l,
					Size:       GLint(arr.Size),
					Type:       arr.Type,
					Normalized: arr.Normalized,
					Stride:     arr.Stride,
					Data:       NewVertexPointer(offset),
				})
			}
		}
	}

	// Restore original state.
	return func() {
		out.Write(ctx, atom.NoID, NewGlBindBuffer(GLenum_GL_ARRAY_BUFFER, c.BoundBuffers.ArrayBuffer))
		for _, id := range ids {
			delete(c.Instances.Buffers, id)
			tmp := atom.Must(atom.AllocData(ctx, s, d, id))
			out.Write(ctx, atom.NoID, NewGlDeleteBuffers(1, tmp.Ptr()).AddRead(tmp.Data()))
		}
	}
}