//
// Book:      OpenGL(R) ES 2.0 Programming Guide
// Authors:   Aaftab Munshi, Dan Ginsburg, Dave Shreiner
// ISBN-10:   0321502795
// ISBN-13:   9780321502797
// Publisher: Addison-Wesley Professional
// URLs:      http://safari.informit.com/9780321563835
//            http://www.opengles-book.com
//

// Simple_Texture2D.c
//
//    This is a simple example that draws a quad with a 2D
//    texture image. The purpose of this example is to demonstrate 
//    the basics of 2D texturing
//
#include <stdlib.h>
#include "Simple_Texture2D.h"

///
// Create a simple 2x2 texture image with four different colors
//
static GLuint CreateSimpleTexture2D( )
{
   // Texture object handle
   GLuint textureId;
   
   // 2x2 Image, 3 bytes per pixel (R, G, B)
   GLubyte pixels[4 * 3] =
   {  
      255,   0,   0, // Red
        0, 255,   0, // Green
        0,   0, 255, // Blue
      255, 255,   0  // Yellow
   };

   // Use tightly packed data
   glPixelStorei ( GL_UNPACK_ALIGNMENT, 1 );

   // Generate a texture object
   glGenTextures ( 1, &textureId );

   // Bind the texture object
   glBindTexture ( GL_TEXTURE_2D, textureId );

   // Load the texture
   glTexImage2D ( GL_TEXTURE_2D, 0, GL_RGB, 2, 2, 0, GL_RGB, GL_UNSIGNED_BYTE, pixels );

   // Set the filtering mode
   glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST );
   glTexParameteri ( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST );

   return textureId;

}


///
// Initialize the shader and program object
//
int stInit ( ESContext *esContext )
{
   STUserData *userData = esContext->userData;
   GLbyte vShaderStr[] =  
      "attribute vec4 a_position;   \n"
      "attribute vec2 a_texCoord;   \n"
      "varying vec2 v_texCoord;     \n"
      "void main()                  \n"
      "{                            \n"
      "   gl_Position = a_position; \n"
      "   v_texCoord = a_texCoord;  \n"
      "}                            \n";
   
   GLbyte fShaderStr[] =  
      "precision mediump float;                            \n"
      "varying vec2 v_texCoord;                            \n"
      "uniform sampler2D s_texture;                        \n"
      "void main()                                         \n"
      "{                                                   \n"
      "  gl_FragColor = texture2D( s_texture, v_texCoord );\n"
      "}                                                   \n";

   GLfloat vVertices[] = { -0.5f,  0.5f, 0.0f,  // Position 0
                            0.0f,  0.0f,        // TexCoord 0 
                           -0.5f, -0.5f, 0.0f,  // Position 1
                            0.0f,  1.0f,        // TexCoord 1
                            0.5f, -0.5f, 0.0f,  // Position 2
                            1.0f,  1.0f,        // TexCoord 2
                            0.5f,  0.5f, 0.0f,  // Position 3
                            1.0f,  0.0f         // TexCoord 3
                         };
   GLushort indices[] = { 0, 1, 2, 0, 2, 3 };

   // Load the shaders and get a linked program object
   userData->programObject = esLoadProgram ( vShaderStr, fShaderStr );

   // Get the attribute locations
   userData->positionLoc = glGetAttribLocation ( userData->programObject, "a_position" );
   userData->texCoordLoc = glGetAttribLocation ( userData->programObject, "a_texCoord" );
   
   // Get the sampler location
   userData->samplerLoc = glGetUniformLocation ( userData->programObject, "s_texture" );

   // Load the texture
   userData->textureId = CreateSimpleTexture2D ();

   // Load vertex data
   glGenBuffers ( 2, userData->vboIds );
   glBindBuffer ( GL_ARRAY_BUFFER, userData->vboIds[0] );
   glBufferData ( GL_ARRAY_BUFFER, sizeof(vVertices),
                  vVertices, GL_STATIC_DRAW);
   glBindBuffer ( GL_ELEMENT_ARRAY_BUFFER, userData->vboIds[1] );
   glBufferData ( GL_ELEMENT_ARRAY_BUFFER, sizeof(indices),
	                indices, GL_STATIC_DRAW );

   glClearColor ( 0.0f, 0.0f, 0.0f, 0.0f );
   return TRUE;
}

///
// Draw a triangle using the shader pair created in Init()
//
#define VTX_POS_SIZE 3
#define VTX_TEX_SIZE 2
#define VTX_STRIDE (5 * sizeof(GLfloat))
void stDraw ( ESContext *esContext )
{
   STUserData *userData = esContext->userData;
   GLuint offset = 0;
      
   // Set the viewport
   glViewport ( 0, 0, esContext->width, esContext->height );
   
   // Clear the color buffer
   glClear ( GL_COLOR_BUFFER_BIT );

   // Use the program object
   glUseProgram ( userData->programObject );

   // Load the vertex position
   glVertexAttribPointer ( userData->positionLoc, VTX_POS_SIZE, GL_FLOAT, 
                           GL_FALSE, VTX_STRIDE, (GLvoid*) offset );
   // Load the texture coordinate
   offset += VTX_POS_SIZE * sizeof(GLfloat);
   glVertexAttribPointer ( userData->texCoordLoc, VTX_TEX_SIZE, GL_FLOAT,
                           GL_FALSE, VTX_STRIDE, (GLvoid*) offset );

   glEnableVertexAttribArray ( userData->positionLoc );
   glEnableVertexAttribArray ( userData->texCoordLoc );

   // Bind the texture
   glActiveTexture ( GL_TEXTURE0 );
   glBindTexture ( GL_TEXTURE_2D, userData->textureId );

   // Set the sampler texture unit to 0
   glUniform1i ( userData->samplerLoc, 0 );

   glDrawElements ( GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, 0 );
}

///
// Cleanup
//
void stShutDown ( ESContext *esContext )
{
   STUserData *userData = esContext->userData;

   // Delete texture object
   glDeleteTextures ( 1, &userData->textureId );

   // Delete VBOs
   glDeleteBuffers ( 2, userData->vboIds );

   // Delete program object
   glDeleteProgram ( userData->programObject );
}