/************************************************************************** * * 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 * without limitation the rights to use, copy, modify, merge, publish, * distribute, sub license, and/or sell copies of the Software, and to * permit persons to whom the Software is furnished to do so, subject to * the following conditions: * * The above copyright notice and this permission notice (including the * next paragraph) shall be included in all copies or substantial portions * of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. * IN NO EVENT SHALL VMWARE AND/OR ITS SUPPLIERS BE LIABLE FOR * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. * **************************************************************************/ /** * @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 */ #include "util/u_debug.h" #include "util/u_math.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; }