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//
// Copyright 2022 The ANGLE Project Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// loadimage_paletted.cpp: Decodes GL_PALETTE_* textures.
#include "image_util/loadimage.h"
#include <type_traits>
#include "common/mathutil.h"
#include "image_util/imageformats.h"
namespace angle
{
namespace
{
template <typename T>
R8G8B8A8 ReadColor(const T *src)
{
gl::ColorF tmp;
T::readColor(&tmp, src);
R8G8B8A8 rgba;
R8G8B8A8::writeColor(&rgba, &tmp);
return rgba;
}
size_t DecodeIndexIntoPalette(const uint8_t *row, size_t i, uint32_t indexBits)
{
switch (indexBits)
{
case 4:
{
// From OES_compressed_paletted_texture, section Additions to
// Chapter 3 of the OpenGL 1.3 Specification (Rasterization):
//
// Texel Data Formats for compressed paletted textures
//
// PALETTE4_xxx:
//
// 7 6 5 4 3 2 1 0
// ---------------
// | 1st | 2nd |
// | texel | texel |
// ---------------
bool even = i % 2 == 0;
return (row[i / 2] >> (even ? 4 : 0)) & 0x0f;
}
case 8:
return row[i];
default:
UNREACHABLE();
return 0;
}
}
R8G8B8A8 DecodeColor(const uint8_t *src,
uint32_t redBlueBits,
uint32_t greenBits,
uint32_t alphaBits)
{
switch (redBlueBits)
{
case 8:
ASSERT(greenBits == 8);
switch (alphaBits)
{
case 0:
return ReadColor<>(reinterpret_cast<const R8G8B8 *>(src));
case 8:
return ReadColor<>(reinterpret_cast<const R8G8B8A8 *>(src));
default:
UNREACHABLE();
break;
}
break;
case 5:
switch (greenBits)
{
case 6:
ASSERT(alphaBits == 0);
return ReadColor<>(reinterpret_cast<const R5G6B5 *>(src));
case 5:
ASSERT(alphaBits == 1);
return ReadColor<>(reinterpret_cast<const R5G5B5A1 *>(src));
default:
UNREACHABLE();
break;
}
break;
case 4:
ASSERT(greenBits == 4 && alphaBits == 4);
return ReadColor<>(reinterpret_cast<const R4G4B4A4 *>(src));
default:
UNREACHABLE();
break;
}
UNREACHABLE();
return R8G8B8A8{0, 0, 0, 255};
}
} // namespace
// See LoadPalettedToRGBA8.
void LoadPalettedToRGBA8Impl(size_t width,
size_t height,
size_t depth,
uint32_t indexBits,
uint32_t redBlueBits,
uint32_t greenBits,
uint32_t alphaBits,
const uint8_t *input,
size_t inputRowPitch,
size_t inputDepthPitch,
uint8_t *output,
size_t outputRowPitch,
size_t outputDepthPitch)
{
size_t colorBytes = (redBlueBits + greenBits + redBlueBits + alphaBits) / 8;
size_t paletteSize = 1 << indexBits;
size_t paletteBytes = paletteSize * colorBytes;
const uint8_t *palette = input;
for (size_t z = 0; z < depth; z++)
{
for (size_t y = 0; y < height; y++)
{
const uint8_t *srcRow =
priv::OffsetDataPointer<uint8_t>(texels, y, z, inputRowPitch, inputDepthPitch);
R8G8B8A8 *dstRow =
priv::OffsetDataPointer<R8G8B8A8>(output, y, z, outputRowPitch, outputDepthPitch);
for (size_t x = 0; x < width; x++)
{
size_t indexIntoPalette = DecodeIndexIntoPalette(srcRow, x, indexBits);
dstRow[x] = DecodeColor(palette + indexIntoPalette * colorBytes, redBlueBits,
greenBits, alphaBits);
}
}
}
}
} // namespace angle