diff options
| -rw-r--r-- | src/gdisp/gdisp.c | 61 |
1 files changed, 42 insertions, 19 deletions
diff --git a/src/gdisp/gdisp.c b/src/gdisp/gdisp.c index 3af31ac2..81d0dd0f 100644 --- a/src/gdisp/gdisp.c +++ b/src/gdisp/gdisp.c @@ -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; - - a = ALPHA_OF(fg) * fg_ratio; - r = RED_OF(fg) * fg_ratio; - g = GREEN_OF(fg) * fg_ratio; - b = BLUE_OF(fg) * fg_ratio; - - a += ALPHA_OF(bg) * bg_ratio; - r += RED_OF(bg) * bg_ratio; - g += GREEN_OF(bg) * bg_ratio; - b += BLUE_OF(bg) * bg_ratio; - - a >>= 8; - r >>= 8; - g >>= 8; - b >>= 8; + uint32_t ratio; + uint32_t a1, r1, g1, b1; + uint32_t a2, r2, g2, b2; + + // Ratio - add one to get 1 to 256 + ratio = (uint32_t)alpha + 1; // 0 to 1 in 0.8 fixed point + + // 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 + + // 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 + + // 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(a, r, g, b); + return ARGB2COLOR(a1, r1, g1, b1); } #else color_t gdispBlendColor(color_t fg, color_t bg, uint8_t alpha) |