Another attempt for T40981, clipping border does not work with GLSL on

ATIs.

This is actually a test to see if this can be enabled on ATI cards.
According to various sources, newer ATI cards supporting GLSL 3.0
support gl_ClippingDistance in shaders, which is the forward compatible
way to do custom clipping.

This fix will bind 6 additional varying variables on ATIs, which may
lead to some shaders not compiling due to limiting out of those
variables, or to performance degradation. Also I do not have an ATI
handy to test.

Having those in mind, this commit may well be reverted later.

Clipping planes are usually 4 (6 is for cube clipping), but making
shaders depend on viewport state is really bad, and would lead to
recompilation, so I took the worst case here to avoid that.
Hopefully driver does some optimization there.

3 files changed, 59 insertions, 20 deletions

diff --git a/source/blender/gpu/intern/gpu_extensions.c b/source/blender/gpu/intern/gpu_extensions.c
index a4fddb3d47c..fc794f91c43 100644
--- a/source/blender/gpu/intern/gpu_extensions.c
+++ b/source/blender/gpu/intern/gpu_extensions.c
@@ -58,6 +58,8 @@
 #  include "BLI_winstuff.h"
 #endif
 
+#define MAX_DEFINE_LENGTH 72
+
 /* Extensions support */
 
 /* extensions used:
@@ -1187,29 +1189,44 @@ static void shader_print_errors(const char *task, char *log, const char *code)
 	fprintf(stderr, "%s\n", log);
 }
 
+static const char *gpu_shader_version(void)
+{
+	/* turn on glsl 1.30 for bicubic bump mapping and ATI clipping support */
+	if (GLEW_VERSION_3_0 &&
+	    (GPU_bicubic_bump_support() || GPU_type_matches(GPU_DEVICE_ATI, GPU_OS_ANY, GPU_DRIVER_ANY)))
+	{
+		return "#version 130\n";
+	}
+
+	return "";
+}
+
+
 static const char *gpu_shader_standard_extensions(void)
 {
 	/* need this extensions for high quality bump mapping */
-	if (GPU_bicubic_bump_support()) {
-		return "#version 130\n"
-		       "#extension GL_ARB_texture_query_lod: enable\n"
-		       "#define BUMP_BICUBIC\n";
-	}
+	if (GPU_bicubic_bump_support())
+		return "#extension GL_ARB_texture_query_lod: enable\n";
 
 	return "";
 }
 
-static const char *gpu_shader_standard_defines(void)
+static void gpu_shader_standard_defines(char defines[MAX_DEFINE_LENGTH])
 {
 	/* some useful defines to detect GPU type */
-	if (GPU_type_matches(GPU_DEVICE_ATI, GPU_OS_ANY, GPU_DRIVER_ANY))
-		return "#define GPU_ATI\n";
+	if (GPU_type_matches(GPU_DEVICE_ATI, GPU_OS_ANY, GPU_DRIVER_ANY)) {
+		strcat(defines, "#define GPU_ATI\n");
+		if (GLEW_VERSION_3_0)
+			strcat(defines, "#define CLIP_WORKAROUND");
+	}
 	else if (GPU_type_matches(GPU_DEVICE_NVIDIA, GPU_OS_ANY, GPU_DRIVER_ANY))
-		return "#define GPU_NVIDIA\n";
+		strcat(defines, "#define GPU_NVIDIA\n");
 	else if (GPU_type_matches(GPU_DEVICE_INTEL, GPU_OS_ANY, GPU_DRIVER_ANY))
-		return "#define GPU_INTEL\n";
-	
-	return "";
+		strcat(defines, "#define GPU_INTEL\n");
+
+	if (GPU_bicubic_bump_support())
+		strcat(defines, "#define BUMP_BICUBIC\n");
+	return;
 }
 
 GPUShader *GPU_shader_create(const char *vertexcode, const char *fragcode, const char *libcode, const char *defines)
@@ -1218,6 +1235,7 @@ GPUShader *GPU_shader_create(const char *vertexcode, const char *fragcode, const
 	GLcharARB log[5000];
 	GLsizei length = 0;
 	GPUShader *shader;
+	char standard_defines[MAX_DEFINE_LENGTH] = "";
 
 	if (!GLEW_ARB_vertex_shader || !GLEW_ARB_fragment_shader)
 		return NULL;
@@ -1239,12 +1257,16 @@ GPUShader *GPU_shader_create(const char *vertexcode, const char *fragcode, const
 		return NULL;
 	}
 
+	gpu_shader_standard_defines(standard_defines);
+
 	if (vertexcode) {
-		const char *source[4];
+		const char *source[5];
+		/* custom limit, may be too small, beware */
 		int num_source = 0;
 
+		source[num_source++] = gpu_shader_version();
 		source[num_source++] = gpu_shader_standard_extensions();
-		source[num_source++] = gpu_shader_standard_defines();
+		source[num_source++] = standard_defines;
 
 		if (defines) source[num_source++] = defines;
 		if (vertexcode) source[num_source++] = vertexcode;
@@ -1265,11 +1287,12 @@ GPUShader *GPU_shader_create(const char *vertexcode, const char *fragcode, const
 	}
 
 	if (fragcode) {
-		const char *source[5];
+		const char *source[6];
 		int num_source = 0;
 
+		source[num_source++] = gpu_shader_version();
 		source[num_source++] = gpu_shader_standard_extensions();
-		source[num_source++] = gpu_shader_standard_defines();
+		source[num_source++] = standard_defines;
 
 		if (defines) source[num_source++] = defines;
 		if (libcode) source[num_source++] = libcode;
diff --git a/source/blender/gpu/shaders/gpu_shader_simple_vert.glsl b/source/blender/gpu/shaders/gpu_shader_simple_vert.glsl
index 830dbec75e2..e094f22637b 100644
--- a/source/blender/gpu/shaders/gpu_shader_simple_vert.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_simple_vert.glsl
@@ -15,6 +15,10 @@ varying vec4 varying_vertex_color;
 varying vec2 varying_texture_coord;
 #endif
 
+#ifdef CLIP_WORKAROUND
+varying float gl_ClipDistance[6];
+#endif
+
 void main()
 {
 	vec4 co = gl_ModelViewMatrix * gl_Vertex;
@@ -29,10 +33,14 @@ void main()
 
 	gl_Position = gl_ProjectionMatrix * co;
 
-#ifndef GPU_ATI
+#ifdef CLIP_WORKAROUND
+	int i;
+	for(i = 0; i < 6; i++)
+		gl_ClipDistance[i] = dot(co, gl_ClipPlane[i]);
+#else
 	// Setting gl_ClipVertex is necessary to get glClipPlane working on NVIDIA
 	// graphic cards, while on ATI it can cause a software fallback.
-	gl_ClipVertex = gl_ModelViewMatrix * gl_Vertex; 
+	gl_ClipVertex = co; 
 #endif 
 
 #ifdef USE_COLOR
diff --git a/source/blender/gpu/shaders/gpu_shader_vertex.glsl b/source/blender/gpu/shaders/gpu_shader_vertex.glsl
index 159e531eb44..96ce00e214f 100644
--- a/source/blender/gpu/shaders/gpu_shader_vertex.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_vertex.glsl
@@ -2,6 +2,10 @@
 varying vec3 varposition;
 varying vec3 varnormal;
 
+#ifdef CLIP_WORKAROUND
+varying float gl_ClipDistance[6];
+#endif
+
 void main()
 {
 	vec4 co = gl_ModelViewMatrix * gl_Vertex;
@@ -10,9 +14,13 @@ void main()
 	varnormal = normalize(gl_NormalMatrix * gl_Normal);
 	gl_Position = gl_ProjectionMatrix * co;
 
-#ifndef GPU_ATI
+#ifdef CLIP_WORKAROUND
+	int i;
+	for(i = 0; i < 6; i++)
+		gl_ClipDistance[i] = dot(co, gl_ClipPlane[i]);
+#else
 	// Setting gl_ClipVertex is necessary to get glClipPlane working on NVIDIA
 	// graphic cards, while on ATI it can cause a software fallback.
-	gl_ClipVertex = gl_ModelViewMatrix * gl_Vertex; 
+	gl_ClipVertex = co; 
 #endif