Xenia-Canary/src/xenia/gpu/xenos.cc

/**
 ******************************************************************************
 * Xenia : Xbox 360 Emulator Research Project                                 *
 ******************************************************************************
 * Copyright 2020 Ben Vanik. All rights reserved.                             *
 * Released under the BSD license - see LICENSE in the root for more details. *
 ******************************************************************************
 */

#include "xenia/gpu/xenos.h"

#include <cmath>

#include "xenia/base/math.h"

namespace xe {
namespace gpu {
namespace xenos {

// Based on X360GammaToLinear and X360LinearToGamma from the Source Engine, with
// additional logic from Direct3D 9 code in game executable disassembly, located
// via the floating-point constants involved.
// https://github.com/ValveSoftware/source-sdk-2013/blob/master/mp/src/mathlib/color_conversion.cpp#L329
// These are provided here in part as a reference for shader translators.

float PWLGammaToLinear(float gamma) {
  // Not found in game executables, so just using the logic similar to that in
  // the Source Engine.
  gamma = xe::saturate_unsigned(gamma);
  float scale, offset;
  // While the compiled code for linear to gamma conversion uses `vcmpgtfp
  // constant, value` comparison (constant > value, or value < constant), it's
  // preferable to use `value >= constant` condition for the higher pieces, as
  // it will never pass for NaN, and in case of NaN, the 0...64/255 case will be
  // selected regardless of whether it's saturated before or after the
  // comparisons (always pre-saturating here, but shader translators may choose
  // to saturate later for convenience), as saturation will flush NaN to 0.
  if (gamma >= 96.0f / 255.0f) {
    if (gamma >= 192.0f / 255.0f) {
      scale = 8.0f / 1024.0f;
      offset = -1024.0f;
    } else {
      scale = 4.0f / 1024.0f;
      offset = -256.0f;
    }
  } else {
    if (gamma >= 64.0f / 255.0f) {
      scale = 2.0f / 1024.0f;
      offset = -64.0f;
    } else {
      scale = 1.0f / 1024.0f;
      offset = 0.0f;
      // No `floor` term in this case in the Source Engine, but for the largest
      // value, 1.0, `floor(255.0f * (1.0f / 1024.0f))` is 0 anyway.
    }
  }
  // Though in the Source Engine, the 1/1024 multiplication is done for the
  // truncated part specifically, pre-baking it into the scale is lossless -
  // both 1024 and `scale` are powers of 2.
  float linear = gamma * ((255.0f * 1024.0f) * scale) + offset;
  // For consistency with linear to gamma, and because it's more logical here
  // (0 rather than 1 at -epsilon), using `trunc` instead of `floor`.
  linear += std::trunc(linear * scale);
  linear *= 1.0f / 1023.0f;
  // Clamping is not necessary (1 * (255 * 8) - 1024 + 7 is exactly 1023).
  return linear;
}

float LinearToPWLGamma(float linear) {
  linear = xe::saturate_unsigned(linear);
  float scale, offset;
  // While the compiled code uses `vcmpgtfp constant, value` comparison
  // (constant > value, or value < constant), it's preferable to use `value >=
  // constant` condition for the higher pieces, as it will never pass for NaN,
  // and in case of NaN, the 0...64/1023 case will be selected regardless of
  // whether it's saturated before or after the comparisons (always
  // pre-saturating here, but shader translators may choose to saturate later
  // for convenience), as saturation will flush NaN to 0.
  if (linear >= 128.0f / 1023.0f) {
    if (linear >= 512.0f / 1023.0f) {
      scale = 1023.0f / 8.0f;
      offset = 128.0f / 255.0f;
    } else {
      scale = 1023.0f / 4.0f;
      offset = 64.0f / 255.0f;
    }
  } else {
    if (linear >= 64.0f / 1023.0f) {
      scale = 1023.0f / 2.0f;
      offset = 32.0f / 255.0f;
    } else {
      scale = 1023.0f;
      offset = 0.0f;
    }
  }
  // The truncation isn't in X360LinearToGamma in the Source Engine, but is
  // there in Direct3D 9 disassembly (the `vrfiz` instructions).
  // It also prevents conversion of 1.0 to 1.0034313725490196078431372549016
  // that's handled via clamping in the Source Engine.
  // 127.875 (1023 / 8) is truncated to 127, which, after scaling, becomes
  // 127 / 255, and when 128 / 255 is added, the result is 1.
  return std::trunc(linear * scale) * (1.0f / 255.0f) + offset;
}

// https://github.com/Microsoft/DirectXTex/blob/master/DirectXTex/DirectXTexConvert.cpp

float Float7e3To32(uint32_t f10) {
  f10 &= 0x3FF;
  if (!f10) {
    return 0.0f;
  }
  uint32_t mantissa = f10 & 0x7F;
  uint32_t exponent = f10 >> 7;
  if (!exponent) {
    // Normalize the value in the resulting float.
    // do { Exponent--; Mantissa <<= 1; } while ((Mantissa & 0x80) == 0)
    uint32_t mantissa_lzcnt = xe::lzcnt(mantissa) - (32 - 8);
    exponent = uint32_t(1 - int32_t(mantissa_lzcnt));
    mantissa = (mantissa << mantissa_lzcnt) & 0x7F;
  }
  uint32_t f32 = ((exponent + 124) << 23) | (mantissa << 3);
  return *reinterpret_cast<const float*>(&f32);
}

// Based on CFloat24 from d3dref9.dll and the 6e4 code from:
// https://github.com/Microsoft/DirectXTex/blob/master/DirectXTex/DirectXTexConvert.cpp
// 6e4 has a different exponent bias allowing [0,512) values, 20e4 allows [0,2).

uint32_t Float32To20e4(float f32, bool round_to_nearest_even) {
  if (!(f32 > 0.0f)) {
    // Positive only, and not -0 or NaN.
    return 0;
  }
  uint32_t f32u32 = *reinterpret_cast<const uint32_t*>(&f32);
  if (f32u32 >= 0x3FFFFFF8) {
    // Saturate.
    return 0xFFFFFF;
  }
  if (f32u32 < 0x38800000) {
    // The number is too small to be represented as a normalized 20e4.
    // Convert it to a denormalized value.
    uint32_t shift = std::min(uint32_t(113 - (f32u32 >> 23)), uint32_t(24));
    f32u32 = (0x800000 | (f32u32 & 0x7FFFFF)) >> shift;
  } else {
    // Rebias the exponent to represent the value as a normalized 20e4.
    f32u32 += 0xC8000000u;
  }
  if (round_to_nearest_even) {
    f32u32 += 3 + ((f32u32 >> 3) & 1);
  }
  return (f32u32 >> 3) & 0xFFFFFF;
}

float Float20e4To32(uint32_t f24) {
  f24 &= 0xFFFFFF;
  if (!f24) {
    return 0.0f;
  }
  uint32_t mantissa = f24 & 0xFFFFF;
  uint32_t exponent = f24 >> 20;
  if (!exponent) {
    // Normalize the value in the resulting float.
    // do { Exponent--; Mantissa <<= 1; } while ((Mantissa & 0x100000) == 0)
    uint32_t mantissa_lzcnt = xe::lzcnt(mantissa) - (32 - 21);
    exponent = uint32_t(1 - int32_t(mantissa_lzcnt));
    mantissa = (mantissa << mantissa_lzcnt) & 0xFFFFF;
  }
  uint32_t f32 = ((exponent + 112) << 23) | (mantissa << 3);
  return *reinterpret_cast<const float*>(&f32);
}

const char* GetColorRenderTargetFormatName(ColorRenderTargetFormat format) {
  switch (format) {
    case ColorRenderTargetFormat::k_8_8_8_8:
      return "k_8_8_8_8";
    case ColorRenderTargetFormat::k_8_8_8_8_GAMMA:
      return "k_8_8_8_8_GAMMA";
    case ColorRenderTargetFormat::k_2_10_10_10:
      return "k_2_10_10_10";
    case ColorRenderTargetFormat::k_2_10_10_10_FLOAT:
      return "k_2_10_10_10_FLOAT";
    case ColorRenderTargetFormat::k_16_16:
      return "k_16_16";
    case ColorRenderTargetFormat::k_16_16_16_16:
      return "k_16_16_16_16";
    case ColorRenderTargetFormat::k_16_16_FLOAT:
      return "k_16_16_FLOAT";
    case ColorRenderTargetFormat::k_16_16_16_16_FLOAT:
      return "k_16_16_16_16_FLOAT";
    case ColorRenderTargetFormat::k_2_10_10_10_AS_10_10_10_10:
      return "k_2_10_10_10_AS_10_10_10_10";
    case ColorRenderTargetFormat::k_2_10_10_10_FLOAT_AS_16_16_16_16:
      return "k_2_10_10_10_FLOAT_AS_16_16_16_16";
    case ColorRenderTargetFormat::k_32_FLOAT:
      return "k_32_FLOAT";
    case ColorRenderTargetFormat::k_32_32_FLOAT:
      return "k_32_32_FLOAT";
    default:
      return "kUnknown";
  }
}

const char* GetDepthRenderTargetFormatName(DepthRenderTargetFormat format) {
  switch (format) {
    case DepthRenderTargetFormat::kD24S8:
      return "kD24S8";
    case DepthRenderTargetFormat::kD24FS8:
      return "kD24FS8";
    default:
      return "kUnknown";
  }
}

}  // namespace xenos
}  // namespace gpu
}  // namespace xe