From 4bdd9ba823da792beae6dd4340b4d320437908cb Mon Sep 17 00:00:00 2001
From: Syndamia <kamen@syndamia.com>
Date: Sat, 14 Mar 2026 22:38:38 +0200
Subject: feat: Implement color opacity

---
 graphics.c | 69 +++++++++++++++++++++++++++++++++++++++-----------------------
 1 file changed, 43 insertions(+), 26 deletions(-)

(limited to 'graphics.c')

diff --git a/graphics.c b/graphics.c
index 2100cc8..71365af 100644
--- a/graphics.c
+++ b/graphics.c
@@ -20,23 +20,35 @@ typedef uint8_t  byte;
 typedef uint16_t byte2;
 typedef uint32_t byte4;
 
-typedef struct RGB {
+typedef struct ARGB {
+	byte a;
 	byte r;
 	byte g;
 	byte b;
-} RGB;
+} ARGB;
 
 void
-RGB_set(RGB* rgb, byte4 color) {
-	rgb->r = (0xFF0000 & color) >> 16;
-	rgb->g = (0x00FF00 & color) >> 8;
-	rgb->b = (0x0000FF & color);
+ARGB_set(ARGB* rgb, byte4 color) {
+	rgb->a = (0xFF000000 & color) >> 24;
+	rgb->r = (0x00FF0000 & color) >> 16;
+	rgb->g = (0x0000FF00 & color) >> 8;
+	rgb->b = (0x000000FF & color);
+}
+
+void
+ARGB_merge(ARGB* bottom, ARGB top) {
+	bottom->a = 255;
+	double perc = top.a / 255.0;
+
+	bottom->r = (bottom->r * (1.0 - perc)) + (top.r * perc);
+	bottom->g = (bottom->g * (1.0 - perc)) + (top.g * perc);
+	bottom->b = (bottom->b * (1.0 - perc)) + (top.b * perc);
 }
 
 typedef struct RGBImage {
 	u32 width;
 	u32 height;
-	RGB* img;
+	ARGB* img;
 } RGBImage;
 
 RGBImage
@@ -44,7 +56,7 @@ RGBImage_new(u32 width, u32 height) {
 	return (RGBImage){
 		.width  = width,
 		.height = height,
-		.img    = malloc(sizeof(RGB) * width * height)
+		.img    = malloc(sizeof(ARGB) * width * height)
 	};
 }
 
@@ -60,7 +72,7 @@ RGBImage_delete(RGBImage* img) {
 	img->img = NULL;
 }
 
-RGB*
+ARGB*
 RGBImage_at(RGBImage img, int row, int col) {
 	return img.img + (row % img.height) * img.width + col % img.width;
 }
@@ -68,7 +80,12 @@ RGBImage_at(RGBImage img, int row, int col) {
 int
 ppm6_write(FILE* f, RGBImage img) {
 	fprintf(f, "P6\n%d %d\n255\n", img.width, img.height);
-	fwrite(img.img, sizeof(*img.img), img.width * img.height, f);
+	size_t size = img.width * img.height;
+	for (size_t i = 0; i < size; ++i) {
+		fputc(img.img[i].r, f);
+		fputc(img.img[i].g, f);
+		fputc(img.img[i].b, f);
+	}
 	return fflush(f);
 }
 
@@ -86,7 +103,7 @@ typedef struct Animation {
 	AnimationEventNode* events;
 } Animation;
 
-typedef RGB (*PixelRenderer)(const Animation* anim, u32 currentFrame, const RGB* pixel, u32 row, u32 col, void* priv);
+typedef ARGB (*PixelRenderer)(const Animation* anim, u32 currentFrame, const ARGB* pixel, u32 row, u32 col, void* priv);
 
 struct AnimationEventNode {
 	AnimationEventNode* next;
@@ -167,9 +184,9 @@ Animation_render(Animation* anim) {
 			for (int r = 0; r < anim->frameBuffer.width; ++r)
 			for (int c = 0; c < anim->frameBuffer.height; ++c) {
 				for (AnimationEventNode* aen = anim->events; aen != NULL && aen->startFrame <= currFrame; aen = aen->next) {
-					RGB* pixel = RGBImage_at(anim->frameBuffer, r, c);
-					RGB newPixel = aen->renderCallback(anim, currFrame, pixel, r, c, aen->privateData);
-					memcpy(pixel, &newPixel, sizeof(RGB));
+					ARGB* pixel = RGBImage_at(anim->frameBuffer, r, c);
+					ARGB newPixel = aen->renderCallback(anim, currFrame, pixel, r, c, aen->privateData);
+					ARGB_merge(pixel, newPixel);
 				}
 
 				AnimationEventNode* prevNode = NULL, *currNode = anim->events;
@@ -194,18 +211,18 @@ Animation_render(Animation* anim) {
 
 ////main////
 
-RGB
-MovingBackground(const Animation* anim, u32 frameIndex, const RGB* currentPixel, u32 r, u32 c, void* priv) {
-	RGB pixel;
+ARGB
+MovingBackground(const Animation* anim, u32 frameIndex, const ARGB* currentPixel, u32 r, u32 c, void* priv) {
+	ARGB pixel;
 
 	r = (r + frameIndex) / 32;
 	c = (c + frameIndex) / 32;
 
 	if ((r + c) % 2 == 0) {
-		RGB_set(&pixel, 0x000000);
+		ARGB_set(&pixel, 0xFF000000);
 	}
 	else {
-		RGB_set(&pixel, 0xFF00FF);
+		ARGB_set(&pixel, 0xFFFF00FF);
 	}
 
 	return pixel;
@@ -217,10 +234,10 @@ struct SquareSettings {
 	byte4 color;
 };
 
-RGB
-Square(const Animation* anim, u32 frameIndex, const RGB* currentPixel, u32 r, u32 c, void* priv) {
-	RGB pixel;
-	memcpy(&pixel, currentPixel, sizeof(RGB));
+ARGB
+Square(const Animation* anim, u32 frameIndex, const ARGB* currentPixel, u32 r, u32 c, void* priv) {
+	ARGB pixel;
+	memcpy(&pixel, currentPixel, sizeof(ARGB));
 
 	struct SquareSettings* set = (struct SquareSettings*)priv;
 
@@ -228,7 +245,7 @@ Square(const Animation* anim, u32 frameIndex, const RGB* currentPixel, u32 r, u3
 	c = (c - frameIndex * 8) % anim->height;
 
 	if (0 <= r && r <= set->width && 0 <= c && c <= set->height) {
-		RGB_set(&pixel, set->color);
+		ARGB_set(&pixel, set->color);
 	}
 
 	return pixel;
@@ -241,12 +258,12 @@ main() {
 	Animation_pushEvent(&anim, 0, 120, MovingBackground, NULL);
 
 	struct SquareSettings s1 = {
-		.width = 20, .height = 20, .color = 0xFFFF00,
+		.width = 20, .height = 20, .color = 0xFFFFFF00,
 	};
 	Animation_pushEvent(&anim, 0, 30, Square, &s1);
 
 	struct SquareSettings s2 = {
-		.width = 10, .height = 25, .color = 0x09FAA5,
+		.width = 10, .height = 25, .color = 0x5009FAA5,
 	};
 	Animation_pushEvent(&anim, 60, 100, Square, &s2);
 
-- 
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