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102 lines
2.5 KiB
102 lines
2.5 KiB
5 years ago
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#include "utils/sdl_bilinear_scale.hpp"
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#include <cstdint>
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#include <memory>
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// Performs bilinear scaling using fixed-width integer math.
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namespace devilution {
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namespace {
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unsigned Frac(unsigned fixedPoint)
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{
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return fixedPoint & 0xffff;
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}
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unsigned ToInt(unsigned fixedPoint)
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{
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return fixedPoint >> 16;
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}
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std::unique_ptr<unsigned[]> CreateMixFactors(unsigned srcSize, unsigned dstSize)
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{
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std::unique_ptr<unsigned[]> result { new unsigned[dstSize + 1] };
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const auto scale = static_cast<unsigned>(65536.0 * static_cast<float>(srcSize - 1) / dstSize);
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unsigned mix = 0;
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for (unsigned i = 0; i <= dstSize; ++i) {
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result[i] = mix;
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mix = Frac(mix) + scale;
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}
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return result;
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};
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std::uint8_t MixColors(std::uint8_t first, std::uint8_t second, unsigned ratio)
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{
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return ToInt((second - first) * ratio) + first;
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}
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} // namespace
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void BilinearScale32(SDL_Surface *src, SDL_Surface *dst)
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{
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const std::unique_ptr<unsigned[]> mixXs = CreateMixFactors(src->w, dst->w);
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const std::unique_ptr<unsigned[]> mixYs = CreateMixFactors(src->h, dst->h);
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const unsigned dgap = dst->pitch - dst->w * 4;
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auto *srcPixels = static_cast<std::uint8_t *>(src->pixels);
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auto *dstPixels = static_cast<std::uint8_t *>(dst->pixels);
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unsigned *curMixY = &mixYs[0];
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unsigned srcY = 0;
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for (unsigned y = 0; y < static_cast<unsigned>(dst->h); ++y) {
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std::uint8_t *s[4] = {
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srcPixels, // Self
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srcPixels + 4, // Right
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srcPixels + src->pitch, // Bottom
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srcPixels + src->pitch + 4 // Bottom right
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};
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unsigned *curMixX = &mixXs[0];
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unsigned srcX = 0;
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for (unsigned x = 0; x < static_cast<unsigned>(dst->w); ++x) {
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const unsigned mixX = Frac(*curMixX);
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const unsigned mixY = Frac(*curMixY);
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for (unsigned channel = 0; channel < 4; ++channel) {
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dstPixels[channel] = MixColors(
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MixColors(s[0][channel], s[1][channel], mixX),
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MixColors(s[2][channel], s[3][channel], mixX),
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mixY);
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}
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++curMixX;
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if (*curMixX > 0) {
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unsigned step = ToInt(*curMixX);
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srcX += step;
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if (srcX <= static_cast<unsigned>(src->w)) {
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step *= 4;
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for (auto &v : s) {
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v += step;
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}
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}
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}
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dstPixels += 4;
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}
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++curMixY;
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if (*curMixY > 0) {
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const unsigned step = ToInt(*curMixY);
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srcY += step;
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if (srcY < static_cast<unsigned>(src->h)) {
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srcPixels += step * src->pitch;
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}
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}
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dstPixels += dgap;
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}
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}
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} // namespace devilution
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