tests/alpha-blending: move unpremult to color_util

More tests are going to need this.

The API is changed to work by copy in and copy out to match the other
color_util API. Hopefully this makes the caller code easier to read.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

tests/alpha-blending-test.c

@@ -94,20 +94,6 @@ premult_color(uint32_t a, uint32_t r, uint32_t g, uint32_t b)
 	return c;
 }
 
-static void
-unpremult_float(struct color_float *cf)
-{
-	int i;
-
-	if (cf->a == 0.0f) {
-		for (i = 0; i < COLOR_CHAN_NUM; i++)
-			cf->rgb[i] = 0.0f;
-	} else {
-		for (i = 0; i < COLOR_CHAN_NUM; i++)
-			cf->rgb[i] /= cf->a;
-	}
-}
-
 static void
 fill_alpha_pattern(struct buffer *buf)
 {
@@ -205,9 +191,9 @@ verify_sRGB_blend_a8r8g8b8(uint32_t bg32, uint32_t fg32, uint32_t dst32,
 	bool ok = true;
 	int i;
 
-	unpremult_float(&bg);
+	bg = color_float_unpremult(bg);
-	unpremult_float(&fg);
+	fg = color_float_unpremult(fg);
-	unpremult_float(&dst);
+	dst = color_float_unpremult(dst);
 
 	if (space == BLEND_LINEAR) {
 		sRGB_linearize(&bg);

tests/color_util.c

@@ -280,6 +280,24 @@ sRGB_delinearize(struct color_float *cf)
 	*cf = color_float_apply_curve(TRANSFER_FN_SRGB_EOTF_INVERSE, *cf);
 }
 
+struct color_float
+color_float_unpremult(struct color_float in)
+{
+	static const struct color_float transparent = {
+		.r = 0.0f, .g = 0.0f, .b = 0.0f, .a = 0.0f,
+	};
+	struct color_float out;
+	int i;
+
+	if (in.a == 0.0f)
+		return transparent;
+
+	for (i = 0; i < COLOR_CHAN_NUM; i++)
+		out.rgb[i] = in.rgb[i] / in.a;
+	out.a = in.a;
+	return out;
+}
+
 /*
  * Returns the result of the matrix-vector multiplication mat * c.
  */

tests/color_util.h

@@ -107,6 +107,9 @@ process_pixel_using_pipeline(enum transfer_fn pre_curve,
 			     const struct color_float *in,
 			     struct color_float *out);
 
+struct color_float
+color_float_unpremult(struct color_float in);
+
 struct color_float
 color_float_apply_matrix(const struct lcmsMAT3 *mat, struct color_float c);