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sw_engine: rectifiy logic wrt overall blendings
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Browse source 
- minor optimization of the unpremultiply logic
- exception handling for the unpremultipy logic for anti-aliasing quality
- appropriate alpha pre/unpre multiplication is applied
- clean code++
- updated doc blending equation

issue: https://github.com/thorvg/thorvg/issues/1944
This commit is contained in:
Hermet Park 2025-07-11 02:16:16 +09:00 • committed by Hermet Park
parent f6a9efcc3f
commit d2b2fb02f0
3 changed files with 105 additions and 113 deletions
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8
inc/thorvg.h
View file

@ -200,15 +200,15 @@ enum class BlendMethod : uint8_t
Normal = 0, ///< Perform the alpha blending(default). S if (Sa == 255), otherwise (Sa * S) + (255 - Sa) * D
Multiply, ///< Takes the RGB channel values from 0 to 255 of each pixel in the top layer and multiples them with the values for the corresponding pixel from the bottom layer. (S * D)
Screen, ///< The values of the pixels in the two layers are inverted, multiplied, and then inverted again. (S + D) - (S * D)
Overlay, ///< Combines Multiply and Screen blend modes. (2 * S * D) if (2 * D < Da), otherwise (Sa * Da) - 2 * (Da - S) * (Sa - D)
Overlay, ///< Combines Multiply and Screen blend modes. (2 * S * D) if (D < 128), otherwise 255 - 2 * (255 - S) * (255 - D)
Darken, ///< Creates a pixel that retains the smallest components of the top and bottom layer pixels. min(S, D)
Lighten, ///< Only has the opposite action of Darken Only. max(S, D)
ColorDodge, ///< Divides the bottom layer by the inverted top layer. D / (255 - S)
ColorBurn, ///< Divides the inverted bottom layer by the top layer, and then inverts the result. 255 - (255 - D) / S
HardLight, ///< The same as Overlay but with the color roles reversed. (2 * S * D) if (S < Sa), otherwise (Sa * Da) - 2 * (Da - S) * (Sa - D)
SoftLight, ///< The same as Overlay but with applying pure black or white does not result in pure black or white. (1 - 2 * S) * (D ^ 2) + (2 * S * D)
HardLight, ///< The same as Overlay but with the color roles reversed. (2 * S * D) if (S < 128), otherwise 255 - 2 * (255 - S) * (255 - D)
SoftLight, ///< The same as Overlay but with applying pure black or white does not result in pure black or white. (255 - 2 * S) * (D * D) + (2 * S * D)
Difference, ///< Subtracts the bottom layer from the top layer or the other way around, to always get a non-negative value. (S - D) if (S > D), otherwise (D - S)
Exclusion, ///< The result is twice the product of the top and bottom layers, subtracted from their sum. s + d - (2 * s * d)
Exclusion, ///< The result is twice the product of the top and bottom layers, subtracted from their sum. S + D - (2 * S * D)
Hue, ///< Reserved. Not supported.
Saturation, ///< Reserved. Not supported.
Color, ///< Reserved. Not supported.

182
src/renderer/sw_engine/tvgSwCommon.h
View file

@ -373,18 +373,34 @@ static inline uint8_t C3(uint32_t c)
return (c);
}
static inline bool UNPREMULTIPLY(uint32_t color, RenderColor& out)
static inline uint32_t PREMULTIPLY(uint32_t c, uint8_t a)
{
out.a = A(color);
if (out.a == 0) return false;
return (c & 0xff000000) + ((((c >> 8) & 0xff) * a) & 0xff00) + ((((c & 0x00ff00ff) * a) >> 8) & 0x00ff00ff);
}
out.r = C1(color) * 255 / out.a;
out.g = C2(color) * 255 / out.a;
out.b = C3(color) * 255 / out.a;
static inline bool BLEND_UPRE(uint32_t c, RenderColor& o)
{
o.a = A(c);
if (o.a == 0) return false;
o.r = C1(c);
o.g = C2(c);
o.b = C3(c);
if (o.a < 255) {
o.r = std::min(o.r * 255u / o.a, 255u);
o.g = std::min(o.g * 255u / o.a, 255u);
o.b = std::min(o.b * 255u / o.a, 255u);
}
return true;
}
static inline uint32_t BLEND_PRE(uint32_t c1, uint32_t c2, uint8_t a)
{
return ALPHA_BLEND(c1, a) + ALPHA_BLEND(c2, 255 - a);
}
static inline uint32_t opBlendInterp(uint32_t s, uint32_t d, uint8_t a)
{
return INTERPOLATE(s, d, a);
@ -411,160 +427,140 @@ static inline uint32_t opBlendDifference(uint32_t s, uint32_t d, TVG_UNUSED uint
{
if (d == 0) return s;
//if (s > d) => s - d
//else => d - s
auto c1 = (C1(s) > C1(d)) ? (C1(s) - C1(d)) : (C1(d) - C1(s));
auto c2 = (C2(s) > C2(d)) ? (C2(s) - C2(d)) : (C2(d) - C2(s));
auto c3 = (C3(s) > C3(d)) ? (C3(s) - C3(d)) : (C3(d) - C3(s));
return JOIN(255, c1, c2, c3);
auto f = [](uint8_t s, uint8_t d) {
return (s > d) ? (s - d) : (d - s);
};
return JOIN(255, f(C1(s), C1(d)), f(C2(s), C2(d)), f(C3(s), C3(d)));
}
static inline uint32_t opBlendExclusion(uint32_t s, uint32_t d, TVG_UNUSED uint8_t a)
{
if (d == 0) return s;
// (s + d) - (2 * s * d)
auto c1 = tvg::clamp(C1(s) + C1(d) - 2 * MULTIPLY(C1(s), C1(d)), 0, 255);
auto c2 = tvg::clamp(C2(s) + C2(d) - 2 * MULTIPLY(C2(s), C2(d)), 0, 255);
auto c3 = tvg::clamp(C3(s) + C3(d) - 2 * MULTIPLY(C3(s), C3(d)), 0, 255);
return JOIN(255, c1, c2, c3);
auto f = [](uint8_t s, uint8_t d) {
return tvg::clamp(s + d - 2 * MULTIPLY(s, d), 0, 255);
};
return JOIN(255, f(C1(s), C1(d)), f(C2(s), C2(d)), f(C3(s), C3(d)));
}
static inline uint32_t opBlendAdd(uint32_t s, uint32_t d, TVG_UNUSED uint8_t a)
{
if (d == 0) return s;
// s + d
auto c1 = std::min(C1(s) + C1(d), 255);
auto c2 = std::min(C2(s) + C2(d), 255);
auto c3 = std::min(C3(s) + C3(d), 255);
return JOIN(255, c1, c2, c3);
auto f = [](uint8_t s, uint8_t d) {
return std::min(s + d, 255);
};
return JOIN(255, f(C1(s), C1(d)), f(C2(s), C2(d)), f(C3(s), C3(d)));
}
static inline uint32_t opBlendScreen(uint32_t s, uint32_t d, TVG_UNUSED uint8_t a)
{
if (d == 0) return s;
// s + d - s * d
auto c1 = C1(s) + C1(d) - MULTIPLY(C1(s), C1(d));
auto c2 = C2(s) + C2(d) - MULTIPLY(C2(s), C2(d));
auto c3 = C3(s) + C3(d) - MULTIPLY(C3(s), C3(d));
return JOIN(255, c1, c2, c3);
auto f = [](uint8_t s, uint8_t d) {
return s + d - MULTIPLY(s, d);
};
return JOIN(255, f(C1(s), C1(d)), f(C2(s), C2(d)), f(C3(s), C3(d)));
}
static inline uint32_t opBlendMultiply(uint32_t s, uint32_t d, TVG_UNUSED uint8_t a)
{
if (d == 0) return s;
RenderColor o;
if (!UNPREMULTIPLY(d, o)) return 0;
if (!BLEND_UPRE(d, o)) return s;
// s * d
auto c1 = MULTIPLY(C1(s), o.r);
auto c2 = MULTIPLY(C2(s), o.g);
auto c3 = MULTIPLY(C3(s), o.b);
return JOIN(255, c1, c2, c3);
auto f = [](uint8_t s, uint8_t d) {
return MULTIPLY(s, d);
};
return BLEND_PRE(JOIN(255, f(C1(s), o.r), f(C2(s), o.g), f(C3(s), o.b)), s, o.a);
}
static inline uint32_t opBlendOverlay(uint32_t s, uint32_t d, TVG_UNUSED uint8_t a)
{
if (d == 0) return s;
RenderColor o;
if (!UNPREMULTIPLY(d, o)) return 0;
if (!BLEND_UPRE(d, o)) return s;
// if (2 * d < da) => 2 * s * d,
// else => 1 - 2 * (1 - s) * (1 - d)
auto c1 = (o.r < 128) ? std::min(255, 2 * MULTIPLY(C1(s), o.r)) : (255 - std::min(255, 2 * MULTIPLY(255 - C1(s), 255 - o.r)));
auto c2 = (o.g < 128) ? std::min(255, 2 * MULTIPLY(C2(s), o.g)) : (255 - std::min(255, 2 * MULTIPLY(255 - C2(s), 255 - o.g)));
auto c3 = (o.b < 128) ? std::min(255, 2 * MULTIPLY(C3(s), o.b)) : (255 - std::min(255, 2 * MULTIPLY(255 - C3(s), 255 - o.b)));
return JOIN(255, c1, c2, c3);
auto f = [](uint8_t s, uint8_t d) {
return (d < 128) ? std::min(255, 2 * MULTIPLY(s, d)) : (255 - std::min(255, 2 * MULTIPLY(255 - s, 255 - d)));
};
return BLEND_PRE(JOIN(255, f(C1(s), o.r), f(C2(s), o.g), f(C3(s), o.b)), s, o.a);
}
static inline uint32_t opBlendDarken(uint32_t s, uint32_t d, TVG_UNUSED uint8_t a)
{
if (d == 0) return s;
RenderColor o;
if (!UNPREMULTIPLY(d, o)) return 0;
if (!BLEND_UPRE(d, o)) return s;
// min(s, d)
auto c1 = std::min(C1(s), o.r);
auto c2 = std::min(C2(s), o.g);
auto c3 = std::min(C3(s), o.b);
return JOIN(255, c1, c2, c3);
auto f = [](uint8_t s, uint8_t d) {
return std::min(s, d);
};
return BLEND_PRE(JOIN(255, f(C1(s), o.r), f(C2(s), o.g), f(C3(s), o.b)), s, o.a);
}
static inline uint32_t opBlendLighten(uint32_t s, uint32_t d, TVG_UNUSED uint8_t a)
{
if (d == 0) return s;
// max(s, d)
auto c1 = std::max(C1(s), C1(d));
auto c2 = std::max(C2(s), C2(d));
auto c3 = std::max(C3(s), C3(d));
return JOIN(255, c1, c2, c3);
auto f = [](uint8_t s, uint8_t d) {
return std::max(s, d);
};
return JOIN(255, f(C1(s), C1(d)), f(C2(s), C2(d)), f(C3(s), C3(d)));
}
static inline uint32_t opBlendColorDodge(uint32_t s, uint32_t d, TVG_UNUSED uint8_t a)
{
if (d == 0) return s;
RenderColor o;
if (!BLEND_UPRE(d, o)) return s;
// d / (1 - s)
s = 0xffffffff - s;
auto c1 = C1(d) == 0 ? 0 : (C1(s) == 0 ? 255 : std::min(C1(d) * 255 / C1(s), 255));
auto c2 = C2(d) == 0 ? 0 : (C2(s) == 0 ? 255 : std::min(C2(d) * 255 / C2(s), 255));
auto c3 = C3(d) == 0 ? 0 : (C3(s) == 0 ? 255 : std::min(C3(d) * 255 / C3(s), 255));
return JOIN(255, c1, c2, c3);
auto f = [](uint8_t s, uint8_t d) {
return d == 0 ? 0 : (s == 255 ? 255 : std::min(d * 255 / (255 - s), 255));
};
return BLEND_PRE(JOIN(255, f(C1(s), o.r), f(C2(s), o.g), f(C3(s), o.b)), s, o.a);
}
static inline uint32_t opBlendColorBurn(uint32_t s, uint32_t d, TVG_UNUSED uint8_t a)
{
if (d == 0) return s;
RenderColor o;
if (!UNPREMULTIPLY(d, o)) o.r = o.g = o.b = 0;
if (!BLEND_UPRE(d, o)) return s;
// 1 - (1 - d) / s
auto ir = 255 - o.r;
auto ig = 255 - o.g;
auto ib = 255 - o.b;
auto f = [](uint8_t s, uint8_t d) {
return d == 255 ? 255 : (s == 0 ? 0 : 255 - std::min((255 - d) * 255 / s, 255));
};
auto c1 = o.r == 255 ? 255 : (C1(s) == 0 ? 0 : 255 - std::min(ir * 255 / C1(s), 255));
auto c2 = o.g == 255 ? 255 : (C2(s) == 0 ? 0 : 255 - std::min(ig * 255 / C2(s), 255));
auto c3 = o.b == 255 ? 255 : (C3(s) == 0 ? 0 : 255 - std::min(ib * 255 / C3(s), 255));
return JOIN(255, c1, c2, c3);
return BLEND_PRE(JOIN(255, f(C1(s), o.r), f(C2(s), o.g), f(C3(s), o.b)), s, o.a);
}
static inline uint32_t opBlendHardLight(uint32_t s, uint32_t d, TVG_UNUSED uint8_t a)
{
if (d == 0) return s;
RenderColor o;
if (!UNPREMULTIPLY(d, o)) o.r = o.g = o.b = 0;
if (!BLEND_UPRE(d, o)) return s;
// if (s < sa), (2 * s * d)
// else (sa * da) - 2 * (da - s) * (sa - d)
auto c1 = (C1(s) < 128) ? std::min(255, 2 * MULTIPLY(C1(s), o.r)) : (255 - std::min(255, 2 * MULTIPLY(255 - C1(s), 255 - o.r)));
auto c2 = (C2(s) < 128) ? std::min(255, 2 * MULTIPLY(C2(s), o.g)) : (255 - std::min(255, 2 * MULTIPLY(255 - C2(s), 255 - o.g)));
auto c3 = (C3(s) < 128) ? std::min(255, 2 * MULTIPLY(C3(s), o.b)) : (255 - std::min(255, 2 * MULTIPLY(255 - C3(s), 255 - o.b)));
return JOIN(255, c1, c2, c3);
auto f = [](uint8_t s, uint8_t d) {
return (s < 128) ? std::min(255, 2 * MULTIPLY(s, d)) : (255 - std::min(255, 2 * MULTIPLY(255 - s, 255 - d)));
};
return BLEND_PRE(JOIN(255, f(C1(s), o.r), f(C2(s), o.g), f(C3(s), o.b)), s, o.a);
}
static inline uint32_t opBlendSoftLight(uint32_t s, uint32_t d, TVG_UNUSED uint8_t a)
{
if (d == 0) return s;
RenderColor o;
if (!UNPREMULTIPLY(d, o)) return 0;
if (!BLEND_UPRE(d, o)) return s;
//(255 - 2 * s) * (d * d) + (2 * s * d)
auto c1 = MULTIPLY(255 - std::min(255, 2 * C1(s)), MULTIPLY(o.r, o.r)) + std::min(255, 2 * MULTIPLY(C1(s), o.r));
auto c2 = MULTIPLY(255 - std::min(255, 2 * C2(s)), MULTIPLY(o.g, o.g)) + std::min(255, 2 * MULTIPLY(C2(s), o.g));
auto c3 = MULTIPLY(255 - std::min(255, 2 * C3(s)), MULTIPLY(o.b, o.b)) + std::min(255, 2 * MULTIPLY(C3(s), o.b));
return JOIN(255, c1, c2, c3);
auto f = [](uint8_t s, uint8_t d) {
return MULTIPLY(255 - std::min(255, 2 * s), MULTIPLY(d, d)) + std::min(255, 2 * MULTIPLY(s, d));
};
return BLEND_PRE(JOIN(255, f(C1(s), o.r), f(C2(s), o.g), f(C3(s), o.b)), s, o.a);
}

28
src/renderer/sw_engine/tvgSwRaster.cpp
View file

@ -591,8 +591,7 @@ static bool _rasterBlendingRle(SwSurface* surface, const SwRle* rle, const Rende
}
} else {
for (auto x = 0; x < len; ++x, ++dst) {
auto tmp = surface->blender(color, *dst, 255);
*dst = INTERPOLATE(tmp, *dst, span->coverage);
*dst = INTERPOLATE(surface->blender(color, *dst, 255), *dst, span->coverage);
}
}
}
@ -733,15 +732,13 @@ static bool _rasterScaledBlendingRleImage(SwSurface* surface, const SwImage& ima
for (uint32_t x = static_cast<uint32_t>(span->x); x < static_cast<uint32_t>(span->x) + span->len; ++x, ++dst) {
SCALED_IMAGE_RANGE_X
auto src = scaleMethod(image.buf32, image.stride, image.w, image.h, sx, sy, miny, maxy, sampleSize);
auto tmp = surface->blender(src, *dst, 255);
*dst = INTERPOLATE(tmp, *dst, A(src));
*dst = INTERPOLATE(surface->blender(src, *dst, 255), *dst, A(src));
}
} else {
for (uint32_t x = static_cast<uint32_t>(span->x); x < static_cast<uint32_t>(span->x) + span->len; ++x, ++dst) {
SCALED_IMAGE_RANGE_X
auto src = scaleMethod(image.buf32, image.stride, image.w, image.h, sx, sy, miny, maxy, sampleSize);
auto tmp = surface->blender(src, *dst, 255);
*dst = INTERPOLATE(tmp, *dst, MULTIPLY(alpha, A(src)));
*dst = INTERPOLATE(surface->blender(src, *dst, 255), *dst, MULTIPLY(alpha, A(src)));
}
}
}
@ -822,8 +819,7 @@ static bool _rasterDirectBlendingRleImage(SwSurface* surface, const SwImage& ima
}
} else {
for (auto x = 0; x < len; ++x, ++dst, ++img) {
auto tmp = surface->blender(*img, *dst, 255);
*dst = INTERPOLATE(tmp, *dst, MULTIPLY(alpha, A(*img)));
*dst = INTERPOLATE(surface->blender(*img, *dst, 255), *dst, MULTIPLY(alpha, A(*img)));
}
}
}
@ -918,8 +914,7 @@ static bool _rasterScaledBlendingImage(SwSurface* surface, const SwImage& image,
for (auto x = bbox.min.x; x < bbox.max.x; ++x, ++dst) {
SCALED_IMAGE_RANGE_X
auto src = scaleMethod(image.buf32, image.stride, image.w, image.h, sx, sy, miny, maxy, sampleSize);
auto tmp = surface->blender(src, *dst, 255);
*dst = INTERPOLATE(tmp, *dst, MULTIPLY(opacity, A(src)));
*dst = INTERPOLATE(surface->blender(src, *dst, 255), *dst, MULTIPLY(opacity, A(src)));
}
}
return true;
@ -1533,9 +1528,11 @@ uint32_t rasterUnpremultiply(uint32_t data)
{
auto a = A(data);
if (a == 255 || a == 0) return data;
auto r = C1(data) * 255 / a;
auto g = C2(data) * 255 / a;
auto b = C3(data) * 255 / a;
uint8_t r = std::min(C1(data) * 255u / a, 255u);
uint8_t g = std::min(C2(data) * 255u / a, 255u);
uint8_t b = std::min(C3(data) * 255u / a, 255u);
return JOIN(a, r, g, b);
}
@ -1571,9 +1568,8 @@ void rasterPremultiply(RenderSurface* surface)
auto dst = buffer;
for (uint32_t x = 0; x < surface->w; ++x, ++dst) {
auto c = *dst;
auto a = (c >> 24);
if (a == 255) continue;
*dst = (c & 0xff000000) + ((((c >> 8) & 0xff) * a) & 0xff00) + ((((c & 0x00ff00ff) * a) >> 8) & 0x00ff00ff);
if (A(c) == 255) continue;
*dst = PREMULTIPLY(c, A(c));
}
}
}