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sw_engine: improve grad quality

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For gradients with fill spread set as repeat,
the lack of anti-aliasing between the last and
the first color caused noticeable jagged edges.
Interpolation was introduced between them,
visually improving the gradient quality.
This commit is contained in:
Mira Grudzinska 2024-06-19 01:53:22 +02:00 • committed by Hermet Park
parent 4a23c39520
commit 98c6d92793
1 changed files with 76 additions and 2 deletions
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78
src/renderer/sw_engine/tvgSwFill.cpp
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@ -63,6 +63,66 @@ static void _calculateCoefficients(const SwFill* fill, uint32_t x, uint32_t y, f
}
static uint32_t _estimateAAMargin(const Fill* fdata)
{
constexpr float marginScalingFactor = 800.0f;
if (fdata->identifier() == TVG_CLASS_ID_RADIAL) {
auto radius = P(static_cast<const RadialGradient*>(fdata))->r;
return mathZero(radius) ? 0 : static_cast<uint32_t>(marginScalingFactor / radius);
}
auto grad = P(static_cast<const LinearGradient*>(fdata));
Point p1 {grad->x1, grad->y1};
Point p2 {grad->x2, grad->y2};
auto length = mathLength(&p1, &p2);
return mathZero(length) ? 0 : static_cast<uint32_t>(marginScalingFactor / length);
}
static void _adjustAAMargin(uint32_t& iMargin, uint32_t index)
{
constexpr float threshold = 0.1f;
constexpr uint32_t iMarginMax = 40;
auto iThreshold = static_cast<uint32_t>(index * threshold);
if (iMargin > iThreshold) iMargin = iThreshold;
if (iMargin > iMarginMax) iMargin = iMarginMax;
}
static inline uint32_t _alphaUnblend(uint32_t c)
{
auto a = (c >> 24);
if (a == 255 || a == 0) return c;
auto invA = 255.0f / static_cast<float>(a);
auto c0 = static_cast<uint8_t>(static_cast<float>((c >> 16) & 0xFF) * invA);
auto c1 = static_cast<uint8_t>(static_cast<float>((c >> 8) & 0xFF) * invA);
auto c2 = static_cast<uint8_t>(static_cast<float>(c & 0xFF) * invA);
return (a << 24) | (c0 << 16) | (c1 << 8) | c2;
}
static void _applyAA(const SwFill* fill, uint32_t begin, uint32_t end)
{
if (begin == 0 || end == 0) return;
auto i = GRADIENT_STOP_SIZE - end;
auto rgbaEnd = _alphaUnblend(fill->ctable[i]);
auto rgbaBegin = _alphaUnblend(fill->ctable[begin]);
auto dt = 1.0f / (begin + end + 1.0f);
float t = dt;
while (i != begin) {
auto dist = 255 - static_cast<int32_t>(255 * t);
auto color = INTERPOLATE(rgbaEnd, rgbaBegin, dist);
fill->ctable[i++] = ALPHA_BLEND((color | 0xff000000), (color >> 24));
if (i == GRADIENT_STOP_SIZE) i = 0;
t += dt;
}
}
static bool _updateColorTable(SwFill* fill, const Fill* fdata, const SwSurface* surface, uint8_t opacity)
{
if (!fill->ctable) {
@ -88,6 +148,11 @@ static bool _updateColorTable(SwFill* fill, const Fill* fdata, const SwSurface*
auto pos = 1.5f * inc;
uint32_t i = 0;
//If repeat is true, anti-aliasing must be applied between the last and the first colors.
auto repeat = fill->spread == FillSpread::Repeat;
uint32_t iAABegin = repeat ? _estimateAAMargin(fdata) : 0;
uint32_t iAAEnd = 0;
fill->ctable[i++] = ALPHA_BLEND(rgba | 0xff000000, a);
while (pos <= pColors->offset) {
@ -97,6 +162,11 @@ static bool _updateColorTable(SwFill* fill, const Fill* fdata, const SwSurface*
}
for (uint32_t j = 0; j < cnt - 1; ++j) {
if (repeat && j == cnt - 2 && iAAEnd == 0) {
iAAEnd = iAABegin;
_adjustAAMargin(iAAEnd, GRADIENT_STOP_SIZE - i);
}
auto curr = colors + j;
auto next = curr + 1;
auto delta = 1.0f / (next->offset - curr->offset);
@ -118,14 +188,18 @@ static bool _updateColorTable(SwFill* fill, const Fill* fdata, const SwSurface*
}
rgba = rgba2;
a = a2;
if (repeat && j == 0) _adjustAAMargin(iAABegin, i - 1);
}
rgba = ALPHA_BLEND((rgba | 0xff000000), a);
for (; i < GRADIENT_STOP_SIZE; ++i)
fill->ctable[i] = rgba;
//Make sure the last color stop is represented at the end of the table
fill->ctable[GRADIENT_STOP_SIZE - 1] = rgba;
//For repeat fill spread apply anti-aliasing between the last and first colors,
//othewise make sure the last color stop is represented at the end of the table.
if (repeat) _applyAA(fill, iAABegin, iAAEnd);
else fill->ctable[GRADIENT_STOP_SIZE - 1] = rgba;
return true;
}