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Update to hacked alpha support - now uses pre-multiplied color blending algorithm

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inmarket 2017-10-10 09:21:06 +10:00
parent c3b484a865
commit 2a249e6140
1 changed files with 39 additions and 16 deletions
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55
src/gdisp/gdisp.c
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@ -3654,26 +3654,49 @@ void gdispGDrawBox(GDisplay *g, coord_t x, coord_t y, coord_t cx, coord_t cy, co
// Note: this will still work with real RGB888
color_t gdispBlendColor(color_t fg, color_t bg, uint8_t alpha)
{
uint16_t fg_ratio = alpha + 1;
uint16_t bg_ratio = 256 - alpha;
uint16_t a, r, g, b;
uint32_t ratio;
uint32_t a1, r1, g1, b1;
uint32_t a2, r2, g2, b2;
a = ALPHA_OF(fg) * fg_ratio;
r = RED_OF(fg) * fg_ratio;
g = GREEN_OF(fg) * fg_ratio;
b = BLUE_OF(fg) * fg_ratio;
// Ratio - add one to get 1 to 256
ratio = (uint32_t)alpha + 1; // 0 to 1 in 0.8 fixed point
a += ALPHA_OF(bg) * bg_ratio;
r += RED_OF(bg) * bg_ratio;
g += GREEN_OF(bg) * bg_ratio;
b += BLUE_OF(bg) * bg_ratio;
// Calculate the pre-multiplied values of r, g, b for the fg color
a1 = ALPHA_OF(fg); // 0 to 1 in 0.8 fixed point
r1 = RED_OF(fg) * a1; // 0 to 1 in 0.16 fixed point
g1 = GREEN_OF(fg) * a1; // 0 to 1 in 0.16 fixed point
b1 = BLUE_OF(fg) * a1; // 0 to 1 in 0.16 fixed point
a >>= 8;
r >>= 8;
g >>= 8;
b >>= 8;
// Calculate the pre-multiplied values of r, g, b for the bg color
a2 = ALPHA_OF(bg); // 0 to 1 in 0.8 fixed point
r2 = RED_OF(bg) * a2; // 0 to 1 in 0.16 fixed point
g2 = GREEN_OF(bg) * a2; // 0 to 1 in 0.16 fixed point
b2 = BLUE_OF(bg) * a2; // 0 to 1 in 0.16 fixed point
return ARGB2COLOR(a, r, g, b);
// Calculate the mixed color values
a1 = ratio * (a1 - a2) + (a2<<8); // 0 to 1 in 0.16 fixed point
if (!a1) return GFXTRANSPARENT;
r1 = ((ratio * (r1 - r2))>>8) + r2; // 0 to 1 in 0.16 fixed point
g1 = ((ratio * (g1 - g2))>>8) + g2; // 0 to 1 in 0.16 fixed point
b1 = ((ratio * (b1 - b2))>>8) + b2; // 0 to 1 in 0.16 fixed point
// Fix precision
#if 1
// Convert back to un-multiplied values
ratio = 0x80000000 / a1; // Divide 1 (0.31 fixed point) by a1 (0.16 fixed point) to get the a1 reciprocal in 0.15 fixed point
a1 >>= 8; // Shift to get back to 0.8 fixed point
r1 = (r1 * ratio) >> 23; // Multiply by ratio to get 0.31 and then shift to get back to 0.8 fixed point
g1 = (g1 * ratio) >> 23; // Multiply by ratio to get 0.31 and then shift to get back to 0.8 fixed point
b1 = (b1 * ratio) >> 23; // Multiply by ratio to get 0.31 and then shift to get back to 0.8 fixed point
#else
// Leave as pre-multiplied values
a1 >>= 8; // Shift to get back to 0.8 fixed point
r1 >>= 8; // Shift to get back to 0.8 fixed point
g1 >>= 8; // Shift to get back to 0.8 fixed point
b1 >>= 8; // Shift to get back to 0.8 fixed point
#endif
return ARGB2COLOR(a1, r1, g1, b1);
}
#else
color_t gdispBlendColor(color_t fg, color_t bg, uint8_t alpha)