| /************************************************************************** |
| * |
| * Copyright 2013 VMware, Inc. |
| * All Rights Reserved. |
| * |
| * Permission is hereby granted, free of charge, to any person obtaining a |
| * copy of this software and associated documentation files (the |
| * "Software"), to deal in the Software without restriction, including |
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| * the following conditions: |
| * |
| * The above copyright notice and this permission notice (including the |
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| * of the Software. |
| * |
| * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS |
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| * |
| **************************************************************************/ |
| |
| |
| /** |
| * @file |
| * Format conversion code for srgb formats. |
| * |
| * Functions for converting from srgb to linear and vice versa. |
| * From http://www.opengl.org/registry/specs/EXT/texture_sRGB.txt: |
| * |
| * srgb->linear: |
| * cl = cs / 12.92, cs <= 0.04045 |
| * cl = ((cs + 0.055)/1.055)^2.4, cs > 0.04045 |
| * |
| * linear->srgb: |
| * if (isnan(cl)) { |
| * Map IEEE-754 Not-a-number to zero. |
| * cs = 0.0; |
| * } else if (cl > 1.0) { |
| * cs = 1.0; |
| * } else if (cl < 0.0) { |
| * cs = 0.0; |
| * } else if (cl < 0.0031308) { |
| * cs = 12.92 * cl; |
| * } else { |
| * cs = 1.055 * pow(cl, 0.41666) - 0.055; |
| * } |
| * |
| * This does not need to be accurate, however at least for d3d10 |
| * (http://msdn.microsoft.com/en-us/library/windows/desktop/dd607323%28v=vs.85%29.aspx): |
| * 1) For srgb->linear, it is required that the error on the srgb side is |
| * not larger than 0.5f, which I interpret that if you map the value back |
| * to srgb from linear using the ideal conversion, it would not be off by |
| * more than 0.5f (that is, it would map to the same 8-bit integer value |
| * as it was before conversion to linear). |
| * 2) linear->srgb is permitted 0.6f which luckily looks like quite a large |
| * error is allowed. |
| * 3) Additionally, all srgb values converted to linear and back must result |
| * in the same value as they were originally. |
| * |
| * @author Roland Scheidegger <sroland@vmware.com> |
| */ |
| |
| |
| #include "util/u_debug.h" |
| |
| #include "lp_bld_type.h" |
| #include "lp_bld_const.h" |
| #include "lp_bld_arit.h" |
| #include "lp_bld_bitarit.h" |
| #include "lp_bld_logic.h" |
| #include "lp_bld_format.h" |
| |
| |
| |
| /** |
| * Convert srgb int values to linear float values. |
| * Several possibilities how to do this, e.g. |
| * - table |
| * - doing the pow() with int-to-float and float-to-int tricks |
| * (http://stackoverflow.com/questions/6475373/optimizations-for-pow-with-const-non-integer-exponent) |
| * - just using standard polynomial approximation |
| * (3rd order polynomial is required for crappy but just sufficient accuracy) |
| * |
| * @param src integer (vector) value(s) to convert |
| * (chan_bits bit values unpacked to 32 bit already). |
| */ |
| LLVMValueRef |
| lp_build_srgb_to_linear(struct gallivm_state *gallivm, |
| struct lp_type src_type, |
| unsigned chan_bits, |
| LLVMValueRef src) |
| { |
| struct lp_type f32_type = lp_type_float_vec(32, src_type.length * 32); |
| struct lp_build_context f32_bld; |
| LLVMValueRef srcf, part_lin, part_pow, is_linear, lin_const, lin_thresh; |
| double coeffs[4] = {0.0023f, |
| 0.0030f / 255.0f, |
| 0.6935f / (255.0f * 255.0f), |
| 0.3012f / (255.0f * 255.0f * 255.0f) |
| }; |
| |
| assert(src_type.width == 32); |
| /* Technically this would work with more bits too but would be inaccurate. */ |
| assert(chan_bits <= 8); |
| |
| lp_build_context_init(&f32_bld, gallivm, f32_type); |
| |
| /* |
| * using polynomial: (src * (src * (src * 0.3012 + 0.6935) + 0.0030) + 0.0023) |
| * ( poly = 0.3012*x^3 + 0.6935*x^2 + 0.0030*x + 0.0023) |
| * (found with octave polyfit and some magic as I couldn't get the error |
| * function right). Using the above mentioned error function, the values stay |
| * within +-0.35, except for the lowest values - hence tweaking linear segment |
| * to cover the first 16 instead of the first 11 values (the error stays |
| * just about acceptable there too). |
| * Hence: lin = src > 15 ? poly : src / 12.6 |
| * This function really only makes sense for vectors, should use LUT otherwise. |
| * All in all (including float conversion) 11 instructions (with sse4.1), |
| * 6 constants (polynomial could be done with 1 instruction less at the cost |
| * of slightly worse dependency chain, fma should also help). |
| */ |
| /* doing the 1/255 mul as part of the approximation */ |
| srcf = lp_build_int_to_float(&f32_bld, src); |
| if (chan_bits != 8) { |
| /* could adjust all the constants instead */ |
| LLVMValueRef rescale_const = lp_build_const_vec(gallivm, f32_type, |
| 255.0f / ((1 << chan_bits) - 1)); |
| srcf = lp_build_mul(&f32_bld, srcf, rescale_const); |
| } |
| lin_const = lp_build_const_vec(gallivm, f32_type, 1.0f / (12.6f * 255.0f)); |
| part_lin = lp_build_mul(&f32_bld, srcf, lin_const); |
| |
| part_pow = lp_build_polynomial(&f32_bld, srcf, coeffs, 4); |
| |
| lin_thresh = lp_build_const_vec(gallivm, f32_type, 15.0f); |
| is_linear = lp_build_compare(gallivm, f32_type, PIPE_FUNC_LEQUAL, srcf, lin_thresh); |
| return lp_build_select(&f32_bld, is_linear, part_lin, part_pow); |
| } |
| |
| |
| /** |
| * Convert linear float values to srgb int values. |
| * Several possibilities how to do this, e.g. |
| * - use table (based on exponent/highest order mantissa bits) and do |
| * linear interpolation (https://gist.github.com/rygorous/2203834) |
| * - Chebyshev polynomial |
| * - Approximation using reciprocals |
| * - using int-to-float and float-to-int tricks for pow() |
| * (http://stackoverflow.com/questions/6475373/optimizations-for-pow-with-const-non-integer-exponent) |
| * |
| * @param src float (vector) value(s) to convert. |
| */ |
| static LLVMValueRef |
| lp_build_linear_to_srgb(struct gallivm_state *gallivm, |
| struct lp_type src_type, |
| unsigned chan_bits, |
| LLVMValueRef src) |
| { |
| LLVMBuilderRef builder = gallivm->builder; |
| struct lp_build_context f32_bld; |
| LLVMValueRef lin_thresh, lin, lin_const, is_linear, tmp, pow_final; |
| |
| lp_build_context_init(&f32_bld, gallivm, src_type); |
| |
| src = lp_build_clamp(&f32_bld, src, f32_bld.zero, f32_bld.one); |
| |
| if (0) { |
| /* |
| * using int-to-float and float-to-int trick for pow(). |
| * This is much more accurate than necessary thanks to the correction, |
| * but it most certainly makes no sense without rsqrt available. |
| * Bonus points if you understand how this works... |
| * All in all (including min/max clamp, conversion) 19 instructions. |
| */ |
| |
| float exp_f = 2.0f / 3.0f; |
| /* some compilers can't do exp2f, so this is exp2f(127.0f/exp_f - 127.0f) */ |
| float exp2f_c = 1.30438178253e+19f; |
| float coeff_f = 0.62996f; |
| LLVMValueRef pow_approx, coeff, x2, exponent, pow_1, pow_2; |
| struct lp_type int_type = lp_int_type(src_type); |
| |
| /* |
| * First calculate approx x^8/12 |
| */ |
| exponent = lp_build_const_vec(gallivm, src_type, exp_f); |
| coeff = lp_build_const_vec(gallivm, src_type, |
| exp2f_c * powf(coeff_f, 1.0f / exp_f)); |
| |
| /* premultiply src */ |
| tmp = lp_build_mul(&f32_bld, coeff, src); |
| /* "log2" */ |
| tmp = LLVMBuildBitCast(builder, tmp, lp_build_vec_type(gallivm, int_type), ""); |
| tmp = lp_build_int_to_float(&f32_bld, tmp); |
| /* multiply for pow */ |
| tmp = lp_build_mul(&f32_bld, tmp, exponent); |
| /* "exp2" */ |
| pow_approx = lp_build_itrunc(&f32_bld, tmp); |
| pow_approx = LLVMBuildBitCast(builder, pow_approx, |
| lp_build_vec_type(gallivm, src_type), ""); |
| |
| /* |
| * Since that pow was inaccurate (like 3 bits, though each sqrt step would |
| * give another bit), compensate the error (which is why we chose another |
| * exponent in the first place). |
| */ |
| /* x * x^(8/12) = x^(20/12) */ |
| pow_1 = lp_build_mul(&f32_bld, pow_approx, src); |
| |
| /* x * x * x^(-4/12) = x^(20/12) */ |
| /* Should avoid using rsqrt if it's not available, but |
| * using x * x^(4/12) * x^(4/12) instead will change error weight */ |
| tmp = lp_build_fast_rsqrt(&f32_bld, pow_approx); |
| x2 = lp_build_mul(&f32_bld, src, src); |
| pow_2 = lp_build_mul(&f32_bld, x2, tmp); |
| |
| /* average the values so the errors cancel out, compensate bias, |
| * we also squeeze the 1.055 mul of the srgb conversion plus the 255.0 mul |
| * for conversion to int in here */ |
| tmp = lp_build_add(&f32_bld, pow_1, pow_2); |
| coeff = lp_build_const_vec(gallivm, src_type, |
| 1.0f / (3.0f * coeff_f) * 0.999852f * |
| powf(1.055f * 255.0f, 4.0f)); |
| pow_final = lp_build_mul(&f32_bld, tmp, coeff); |
| |
| /* x^(5/12) = rsqrt(rsqrt(x^20/12)) */ |
| if (lp_build_fast_rsqrt_available(src_type)) { |
| pow_final = lp_build_fast_rsqrt(&f32_bld, |
| lp_build_fast_rsqrt(&f32_bld, pow_final)); |
| } |
| else { |
| pow_final = lp_build_sqrt(&f32_bld, lp_build_sqrt(&f32_bld, pow_final)); |
| } |
| pow_final = lp_build_add(&f32_bld, pow_final, |
| lp_build_const_vec(gallivm, src_type, -0.055f * 255.0f)); |
| } |
| |
| else { |
| /* |
| * using "rational polynomial" approximation here. |
| * Essentially y = a*x^0.375 + b*x^0.5 + c, with also |
| * factoring in the 255.0 mul and the scaling mul. |
| * (a is closer to actual value so has higher weight than b.) |
| * Note: the constants are magic values. They were found empirically, |
| * possibly could be improved but good enough (be VERY careful with |
| * error metric if you'd want to tweak them, they also MUST fit with |
| * the crappy polynomial above for srgb->linear since it is required |
| * that each srgb value maps back to the same value). |
| * This function has an error of max +-0.17. Not sure this is actually |
| * enough, we require +-0.6 but that may include the +-0.5 from integer |
| * conversion. Seems to pass all relevant tests though... |
| * For the approximated srgb->linear values the error is naturally larger |
| * (+-0.42) but still accurate enough (required +-0.5 essentially). |
| * All in all (including min/max clamp, conversion) 15 instructions. |
| * FMA would help (minus 2 instructions). |
| */ |
| |
| LLVMValueRef x05, x0375, a_const, b_const, c_const, tmp2; |
| |
| if (lp_build_fast_rsqrt_available(src_type)) { |
| tmp = lp_build_fast_rsqrt(&f32_bld, src); |
| x05 = lp_build_mul(&f32_bld, src, tmp); |
| } |
| else { |
| /* |
| * I don't really expect this to be practical without rsqrt |
| * but there's no reason for triple punishment so at least |
| * save the otherwise resulting division and unnecessary mul... |
| */ |
| x05 = lp_build_sqrt(&f32_bld, src); |
| } |
| |
| tmp = lp_build_mul(&f32_bld, x05, src); |
| if (lp_build_fast_rsqrt_available(src_type)) { |
| x0375 = lp_build_fast_rsqrt(&f32_bld, lp_build_fast_rsqrt(&f32_bld, tmp)); |
| } |
| else { |
| x0375 = lp_build_sqrt(&f32_bld, lp_build_sqrt(&f32_bld, tmp)); |
| } |
| |
| a_const = lp_build_const_vec(gallivm, src_type, 0.675f * 1.0622 * 255.0f); |
| b_const = lp_build_const_vec(gallivm, src_type, 0.325f * 1.0622 * 255.0f); |
| c_const = lp_build_const_vec(gallivm, src_type, -0.0620f * 255.0f); |
| |
| tmp = lp_build_mul(&f32_bld, a_const, x0375); |
| tmp2 = lp_build_mad(&f32_bld, b_const, x05, c_const); |
| pow_final = lp_build_add(&f32_bld, tmp, tmp2); |
| } |
| |
| /* linear part is easy */ |
| lin_const = lp_build_const_vec(gallivm, src_type, 12.92f * 255.0f); |
| lin = lp_build_mul(&f32_bld, src, lin_const); |
| |
| lin_thresh = lp_build_const_vec(gallivm, src_type, 0.0031308f); |
| is_linear = lp_build_compare(gallivm, src_type, PIPE_FUNC_LEQUAL, src, lin_thresh); |
| tmp = lp_build_select(&f32_bld, is_linear, lin, pow_final); |
| |
| if (chan_bits != 8) { |
| /* could adjust all the constants instead */ |
| LLVMValueRef rescale_const = lp_build_const_vec(gallivm, src_type, |
| ((1 << chan_bits) - 1) / 255.0f); |
| tmp = lp_build_mul(&f32_bld, tmp, rescale_const); |
| } |
| |
| f32_bld.type.sign = 0; |
| return lp_build_iround(&f32_bld, tmp); |
| } |
| |
| |
| /** |
| * Convert linear float soa values to packed srgb AoS values. |
| * This only handles packed formats which are 4x8bit in size |
| * (rgba and rgbx plus swizzles), and 16bit 565-style formats |
| * with no alpha. (In the latter case the return values won't be |
| * fully packed, it will look like r5g6b5x16r5g6b5x16...) |
| * |
| * @param src float SoA (vector) values to convert. |
| */ |
| LLVMValueRef |
| lp_build_float_to_srgb_packed(struct gallivm_state *gallivm, |
| const struct util_format_description *dst_fmt, |
| struct lp_type src_type, |
| LLVMValueRef *src) |
| { |
| LLVMBuilderRef builder = gallivm->builder; |
| unsigned chan; |
| struct lp_build_context f32_bld; |
| struct lp_type int32_type = lp_int_type(src_type); |
| LLVMValueRef tmpsrgb[4], alpha, dst; |
| |
| lp_build_context_init(&f32_bld, gallivm, src_type); |
| |
| /* rgb is subject to linear->srgb conversion, alpha is not */ |
| for (chan = 0; chan < 3; chan++) { |
| unsigned chan_bits = dst_fmt->channel[dst_fmt->swizzle[chan]].size; |
| tmpsrgb[chan] = lp_build_linear_to_srgb(gallivm, src_type, chan_bits, src[chan]); |
| } |
| /* |
| * can't use lp_build_conv since we want to keep values as 32bit |
| * here so we can interleave with rgb to go from SoA->AoS. |
| */ |
| alpha = lp_build_clamp_zero_one_nanzero(&f32_bld, src[3]); |
| alpha = lp_build_mul(&f32_bld, alpha, |
| lp_build_const_vec(gallivm, src_type, 255.0f)); |
| tmpsrgb[3] = lp_build_iround(&f32_bld, alpha); |
| |
| dst = lp_build_zero(gallivm, int32_type); |
| for (chan = 0; chan < dst_fmt->nr_channels; chan++) { |
| if (dst_fmt->swizzle[chan] <= PIPE_SWIZZLE_W) { |
| unsigned ls; |
| LLVMValueRef shifted, shift_val; |
| ls = dst_fmt->channel[dst_fmt->swizzle[chan]].shift; |
| shift_val = lp_build_const_int_vec(gallivm, int32_type, ls); |
| shifted = LLVMBuildShl(builder, tmpsrgb[chan], shift_val, ""); |
| dst = LLVMBuildOr(builder, dst, shifted, ""); |
| } |
| } |
| return dst; |
| } |
