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.

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)

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);
 }

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;
 		}
 	}

intern/cycles/kernel/svm/svm_image.h

@@ -50,7 +50,7 @@ __device_inline float svm_image_texture_frac(float x, int *ix)
 	return x - (float)i;
 }
 
-__device float4 svm_image_texture(KernelGlobals *kg, int id, float x, float y, uint srgb)
+__device float4 svm_image_texture(KernelGlobals *kg, int id, float x, float y, uint srgb, uint use_alpha)
 {
 	/* first slots are used by float textures, which are not supported here */
 	if(id < TEX_NUM_FLOAT_IMAGES)
@@ -88,6 +88,13 @@ __device float4 svm_image_texture(KernelGlobals *kg, int id, float x, float y, u
 	r += ty*(1.0f - tx)*svm_image_texture_read(kg, offset + ix + niy*width);
 	r += ty*tx*svm_image_texture_read(kg, offset + nix + niy*width);
 
+	if(use_alpha && r.w != 1.0f && r.w != 0.0f) {
+		float invw = 1.0f/r.w;
+		r.x *= invw;
+		r.y *= invw;
+		r.z *= invw;
+	}
+
 	if(srgb) {
 		r.x = color_srgb_to_scene_linear(r.x);
 		r.y = color_srgb_to_scene_linear(r.y);
@@ -99,7 +106,7 @@ __device float4 svm_image_texture(KernelGlobals *kg, int id, float x, float y, u
 
 #else
 
-__device float4 svm_image_texture(KernelGlobals *kg, int id, float x, float y, uint srgb)
+__device float4 svm_image_texture(KernelGlobals *kg, int id, float x, float y, uint srgb, uint use_alpha)
 {
 	float4 r;
 
@@ -222,6 +229,13 @@ __device float4 svm_image_texture(KernelGlobals *kg, int id, float x, float y, u
 	}
 #endif
 
+	if(use_alpha && r.w != 1.0f && r.w != 0.0f) {
+		float invw = 1.0f/r.w;
+		r.x *= invw;
+		r.y *= invw;
+		r.z *= invw;
+	}
+
 	if(srgb) {
 		r.x = color_srgb_to_scene_linear(r.x);
 		r.y = color_srgb_to_scene_linear(r.y);
@@ -241,7 +255,8 @@ __device void svm_node_tex_image(KernelGlobals *kg, ShaderData *sd, float *stack
 	decode_node_uchar4(node.z, &co_offset, &out_offset, &alpha_offset, &srgb);
 
 	float3 co = stack_load_float3(stack, co_offset);
-	float4 f = svm_image_texture(kg, id, co.x, co.y, srgb);
+	uint use_alpha = stack_valid(alpha_offset);
+	float4 f = svm_image_texture(kg, id, co.x, co.y, srgb, use_alpha);
 
 	if(stack_valid(out_offset))
 		stack_store_float3(stack, out_offset, make_float3(f.x, f.y, f.z));
@@ -322,13 +337,14 @@ __device void svm_node_tex_image_box(KernelGlobals *kg, ShaderData *sd, float *s
 	uint id = node.y;
 
 	float4 f = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
+	uint use_alpha = stack_valid(alpha_offset);
 
 	if(weight.x > 0.0f)
-		f += weight.x*svm_image_texture(kg, id, co.y, co.z, srgb);
+		f += weight.x*svm_image_texture(kg, id, co.y, co.z, srgb, use_alpha);
 	if(weight.y > 0.0f)
-		f += weight.y*svm_image_texture(kg, id, co.x, co.z, srgb);
+		f += weight.y*svm_image_texture(kg, id, co.x, co.z, srgb, use_alpha);
 	if(weight.z > 0.0f)
-		f += weight.z*svm_image_texture(kg, id, co.y, co.x, srgb);
+		f += weight.z*svm_image_texture(kg, id, co.y, co.x, srgb, use_alpha);
 
 	if(stack_valid(out_offset))
 		stack_store_float3(stack, out_offset, make_float3(f.x, f.y, f.z));
@@ -355,7 +371,8 @@ __device void svm_node_tex_environment(KernelGlobals *kg, ShaderData *sd, float
 	else
 		uv = direction_to_mirrorball(co);
 
-	float4 f = svm_image_texture(kg, id, uv.x, uv.y, srgb);
+	uint use_alpha = stack_valid(alpha_offset);
+	float4 f = svm_image_texture(kg, id, uv.x, uv.y, srgb, use_alpha);
 
 	if(stack_valid(out_offset))
 		stack_store_float3(stack, out_offset, make_float3(f.x, f.y, f.z));