Fix #34679: cycles image texture alpha fringes. New rule is now that color output

will not give straight RGB values if the alpha output is used, so that mixing with
a transparent BSDF gives the correct result.

3 files changed, 21 insertions, 5 deletions

diff --git a/intern/cycles/kernel/shaders/node_color.h b/intern/cycles/kernel/shaders/node_color.h
index 80786e4e369..c6b5d740f6a 100644
--- a/intern/cycles/kernel/shaders/node_color.h
+++ b/intern/cycles/kernel/shaders/node_color.h
@@ -48,6 +48,14 @@ color color_scene_linear_to_srgb(color c)
 		color_scene_linear_to_srgb(c[2]));
 }
 
+color color_unpremultiply(color c, float alpha)
+{
+	if(alpha != 1.0 && alpha != 0.0)
+		return c/alpha;
+
+	return c;
+}
+
 /* Color Operations */
 
 color rgb_to_hsv(color rgb)
diff --git a/intern/cycles/kernel/shaders/node_environment_texture.osl b/intern/cycles/kernel/shaders/node_environment_texture.osl
index 33b30a27ee1..36b2f755c20 100644
--- a/intern/cycles/kernel/shaders/node_environment_texture.osl
+++ b/intern/cycles/kernel/shaders/node_environment_texture.osl
@@ -66,6 +66,9 @@ shader node_environment_texture(
 	/* todo: use environment for better texture filtering of equirectangular */
 	Color = (color)texture(filename, p[0], 1.0 - p[1], "wrap", "periodic", "alpha", Alpha);
 
+	if (isconnected(Alpha))
+		Color = color_unpremultiply(Color, Alpha);
+
 	if (color_space == "sRGB")
 		Color = color_srgb_to_scene_linear(Color);
 }
diff --git a/intern/cycles/kernel/shaders/node_image_texture.osl b/intern/cycles/kernel/shaders/node_image_texture.osl
index c94a3f7e76a..c7ec8726ae2 100644
--- a/intern/cycles/kernel/shaders/node_image_texture.osl
+++ b/intern/cycles/kernel/shaders/node_image_texture.osl
@@ -19,10 +19,13 @@
 #include "stdosl.h"
 #include "node_color.h"
 
-color image_texture_lookup(string filename, string color_space, float u, float v, output float Alpha)
+color image_texture_lookup(string filename, string color_space, float u, float v, output float Alpha, int use_alpha)
 {
 	color rgb = (color)texture(filename, u, 1.0 - v, "wrap", "periodic", "alpha", Alpha);
 
+	if (use_alpha)
+		rgb = color_unpremultiply(rgb, Alpha);
+
 	if (color_space == "sRGB")
 		rgb = color_srgb_to_scene_linear(rgb);
 
@@ -44,9 +47,11 @@ shader node_image_texture(
 
 	if (use_mapping)
 		p = transform(mapping, p);
+	
+	int use_alpha = isconnected(Alpha);
 
 	if (projection == "Flat") {
-		Color = image_texture_lookup(filename, color_space, p[0], p[1], Alpha);
+		Color = image_texture_lookup(filename, color_space, p[0], p[1], Alpha, use_alpha);
 	}
 	else if (projection == "Box") {
 		/* object space normal */
@@ -111,15 +116,15 @@ shader node_image_texture(
 		float tmp_alpha;
 
 		if (weight[0] > 0.0) {
-			Color += weight[0] * image_texture_lookup(filename, color_space, p[1], p[2], tmp_alpha);
+			Color += weight[0] * image_texture_lookup(filename, color_space, p[1], p[2], tmp_alpha, use_alpha);
 			Alpha += weight[0] * tmp_alpha;
 		}
 		if (weight[1] > 0.0) {
-			Color += weight[1] * image_texture_lookup(filename, color_space, p[0], p[2], tmp_alpha);
+			Color += weight[1] * image_texture_lookup(filename, color_space, p[0], p[2], tmp_alpha, use_alpha);
 			Alpha += weight[1] * tmp_alpha;
 		}
 		if (weight[2] > 0.0) {
-			Color += weight[2] * image_texture_lookup(filename, color_space, p[1], p[0], tmp_alpha);
+			Color += weight[2] * image_texture_lookup(filename, color_space, p[1], p[0], tmp_alpha, use_alpha);
 			Alpha += weight[2] * tmp_alpha;
 		}
 	}