OpenGL: further wireframe shaders

As seen at #bcon16

Geometry shader version is automatically used on modern GL runtimes. Legacy version is used on pre-3.2 systems (Mac, Mesa compat profile). They have the same inputs and visual result.

TODO: specialized versions that are less flexible -- draw ALL edges or draw JUST silhouette edges.

Part of T49165

source/blender/gpu/CMakeLists.txt

@@ -159,6 +159,8 @@ data_to_c_simple(shaders/gpu_shader_2D_point_uniform_size_outline_smooth_vert.gl
 data_to_c_simple(shaders/gpu_shader_2D_point_uniform_size_varying_color_outline_smooth_vert.glsl SRC)
 
 data_to_c_simple(shaders/gpu_shader_edges_front_back_persp_vert.glsl SRC)
+data_to_c_simple(shaders/gpu_shader_edges_front_back_persp_geom.glsl SRC)
+data_to_c_simple(shaders/gpu_shader_edges_front_back_persp_legacy_vert.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_edges_front_back_ortho_vert.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_text_vert.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_text_frag.glsl SRC)

source/blender/gpu/intern/gpu_shader.c

@@ -79,6 +79,8 @@ extern char datatoc_gpu_shader_2D_point_uniform_size_outline_smooth_vert_glsl[];
 extern char datatoc_gpu_shader_2D_point_uniform_size_varying_color_outline_smooth_vert_glsl[];
 
 extern char datatoc_gpu_shader_edges_front_back_persp_vert_glsl[];
+extern char datatoc_gpu_shader_edges_front_back_persp_geom_glsl[];
+extern char datatoc_gpu_shader_edges_front_back_persp_legacy_vert_glsl[];
 extern char datatoc_gpu_shader_edges_front_back_ortho_vert_glsl[];
 extern char datatoc_gpu_shader_text_vert_glsl[];
 extern char datatoc_gpu_shader_text_frag_glsl[];
@@ -671,10 +673,20 @@ GPUShader *GPU_shader_get_builtin_shader(GPUBuiltinShader shader)
 			break;
 		case GPU_SHADER_EDGES_FRONT_BACK_PERSP:
 			if (!GG.shaders.edges_front_back_persp)
-				GG.shaders.edges_front_back_persp = GPU_shader_create(
-				        datatoc_gpu_shader_edges_front_back_persp_vert_glsl,
-				        datatoc_gpu_shader_flat_color_alpha_test_0_frag_glsl,
-				        NULL, NULL, NULL, 0, 0, 0);
+				if (GLEW_VERSION_3_2) {
+					/* this version is magical but slooow */
+					GG.shaders.edges_front_back_persp = GPU_shader_create(
+					        datatoc_gpu_shader_edges_front_back_persp_vert_glsl,
+					        datatoc_gpu_shader_flat_color_frag_glsl,
+					        datatoc_gpu_shader_edges_front_back_persp_geom_glsl,
+					        NULL, NULL, 0, 0, 0);
+				}
+				else {
+					GG.shaders.edges_front_back_persp = GPU_shader_create(
+					        datatoc_gpu_shader_edges_front_back_persp_legacy_vert_glsl,
+					        datatoc_gpu_shader_flat_color_alpha_test_0_frag_glsl,
+					        NULL, NULL, NULL, 0, 0, 0);
+				}
 			retval = GG.shaders.edges_front_back_persp;
 			break;
 		case GPU_SHADER_EDGES_FRONT_BACK_ORTHO:

source/blender/gpu/shaders/gpu_shader_edges_front_back_persp_geom.glsl

@@ -0,0 +1,60 @@
+
+// Draw "fancy" wireframe, displaying front-facing, back-facing and
+// silhouette lines differently.
+// Mike Erwin, April 2015
+
+// After working with this shader a while, convinced we should make
+// separate shaders for perpective & ortho. (Oct 2016)
+
+// Due to perspective, the line segment's endpoints might disagree on
+// whether the adjacent faces are front facing. This geometry shader
+// decides which edge type to use if endpoints disagree.
+
+uniform mat4 ProjectionMatrix;
+
+uniform bool drawFront = true;
+uniform bool drawBack = true;
+uniform bool drawSilhouette = true;
+
+uniform vec4 frontColor;
+uniform vec4 backColor;
+uniform vec4 silhouetteColor;
+
+layout(lines) in;
+layout(line_strip, max_vertices = 2) out;
+
+in vec4 MV_pos[];
+in float edgeClass[];
+
+flat out vec4 finalColor;
+
+void emitLine(vec4 color)
+{
+	gl_Position = ProjectionMatrix * MV_pos[0];
+	EmitVertex();
+	gl_Position = ProjectionMatrix * MV_pos[1];
+	finalColor = color;
+	EmitVertex();
+	EndPrimitive();
+}
+
+void main()
+{
+	float finalEdgeClass = max(edgeClass[0], edgeClass[1]);
+
+	if (finalEdgeClass > 0.0f) {
+		// front-facing edge
+		if (drawFront)
+			emitLine(frontColor);	
+	}
+	else if (finalEdgeClass < 0.0f) {
+		// back-facing edge
+		if (drawBack)
+			emitLine(backColor);
+	}
+	else {
+		// exactly one face is front-facing, silhouette edge
+		if (drawSilhouette)
+			emitLine(silhouetteColor);
+	}
+}

source/blender/gpu/shaders/gpu_shader_edges_front_back_persp_legacy_vert.glsl

@@ -0,0 +1,78 @@
+
+// Draw "fancy" wireframe, displaying front-facing, back-facing and
+// silhouette lines differently.
+// Mike Erwin, April 2015
+
+// After working with this shader a while, convinced we should make
+// separate shaders for perpective & ortho. (Oct 2016)
+
+// This shader is an imperfect stepping stone until all platforms are
+// ready for geometry shaders.
+
+// Due to perspective, the line segment's endpoints might disagree on
+// whether the adjacent faces are front facing. Need to use a geometry
+// shader or pass in an extra position attribute (the other endpoint)
+// to do this properly.
+
+uniform bool drawFront = true;
+uniform bool drawBack = true;
+uniform bool drawSilhouette = true;
+
+uniform vec4 frontColor;
+uniform vec4 backColor;
+uniform vec4 silhouetteColor;
+
+uniform mat4 ModelViewMatrix;
+uniform mat4 ModelViewProjectionMatrix;
+uniform mat3 NormalMatrix;
+
+#if __VERSION__ == 120
+	attribute vec3 pos;
+
+	// normals of faces this edge joins (object coords)
+	attribute vec3 N1;
+	attribute vec3 N2;
+
+	flat varying vec4 finalColor;
+#else
+	in vec3 pos;
+
+	// normals of faces this edge joins (object coords)
+	in vec3 N1;
+	in vec3 N2;
+
+	flat out vec4 finalColor;
+#endif
+
+// TODO: in float angle; // [-pi .. +pi], + peak, 0 flat, - valley
+
+// to discard an entire line, set its color to invisible
+// (must have GL_BLEND enabled, or discard in fragment shader)
+const vec4 invisible = vec4(0.0);
+
+bool front(vec3 N)
+{
+	vec4 xformed = ModelViewMatrix * vec4(pos, 1.0);
+	return dot(NormalMatrix * N, normalize(-xformed.xyz)) > 0.0;
+}
+
+void main()
+{
+	bool face_1_front = front(N1);
+	bool face_2_front = front(N2);
+
+	gl_Position = ModelViewProjectionMatrix * vec4(pos, 1.0);
+
+	if (face_1_front && face_2_front) {
+		// front-facing edge
+		finalColor = drawFront ? frontColor : invisible;
+	}
+	else if (face_1_front || face_2_front) {
+		// exactly one face is front-facing, silhouette edge
+		finalColor = drawSilhouette ? silhouetteColor : invisible;
+	}
+	else {
+		// back-facing edge
+		finalColor = drawBack ? backColor : invisible;
+	}
+}

source/blender/gpu/shaders/gpu_shader_edges_front_back_persp_vert.glsl

@@ -6,73 +6,39 @@
 // After working with this shader a while, convinced we should make
 // separate shaders for perpective & ortho. (Oct 2016)
 
-// This shader is an imperfect stepping stone until all platforms are
-// ready for geometry shaders.
-
 // Due to perspective, the line segment's endpoints might disagree on
-// whether the adjacent faces are front facing. Need to use a geometry
-// shader or pass in an extra position attribute (the other endpoint)
-// to do this properly.
-
-uniform bool drawFront = true;
-uniform bool drawBack = true;
-uniform bool drawSilhouette = true;
-
-uniform vec4 frontColor;
-uniform vec4 backColor;
-uniform vec4 silhouetteColor;
+// whether the adjacent faces are front facing. We use a geometry
+// shader to resolve this properly.
 
 uniform mat4 ModelViewMatrix;
-uniform mat4 ModelViewProjectionMatrix;
 uniform mat3 NormalMatrix;
 
-#if __VERSION__ == 120
-	attribute vec3 pos;
+in vec3 pos;
+in vec3 N1, N2; // normals of faces this edge joins (object coords)
 
-	// normals of faces this edge joins (object coords)
-	attribute vec3 N1;
-	attribute vec3 N2;
-
-	flat varying vec4 finalColor;
-#else
-	in vec3 pos;
-
-	// normals of faces this edge joins (object coords)
-	in vec3 N1;
-	in vec3 N2;
-
-	flat out vec4 finalColor;
-#endif
+out vec4 MV_pos;
+out float edgeClass;
 
 // TODO: in float angle; // [-pi .. +pi], + peak, 0 flat, - valley
 
-// to discard an entire line, set its color to invisible
-// (must have GL_BLEND enabled, or discard in fragment shader)
-const vec4 invisible = vec4(0.0);
-
-bool front(vec3 N)
+bool front(vec3 N, vec3 eye)
 {
-	vec4 xformed = ModelViewMatrix * vec4(pos, 1.0);
-	return dot(NormalMatrix * N, normalize(-xformed.xyz)) > 0.0;
+	return dot(NormalMatrix * N, eye) > 0.0;
 }
 
 void main()
 {
-	bool face_1_front = front(N1);
-	bool face_2_front = front(N2);
+	MV_pos = ModelViewMatrix * vec4(pos, 1.0);
 
-	gl_Position = ModelViewProjectionMatrix * vec4(pos, 1.0);
+	vec3 eye = normalize(-MV_pos.xyz);
 
-	if (face_1_front && face_2_front) {
-		// front-facing edge
-		finalColor = drawFront ? frontColor : invisible;
-	}
-	else if (face_1_front || face_2_front) {
-		// exactly one face is front-facing, silhouette edge
-		finalColor = drawSilhouette ? silhouetteColor : invisible;
-	}
-	else {
-		// back-facing edge
-		finalColor = drawBack ? backColor : invisible;
-	}
+	bool face_1_front = front(N1, eye);
+	bool face_2_front = front(N2, eye);
+
+	if (face_1_front && face_2_front)
+		edgeClass = 1.0; // front-facing edge
+	else if (face_1_front || face_2_front)
+		edgeClass = 0.0; // exactly one face is front-facing, silhouette edge
+	else
+		edgeClass = -1.0; // back-facing edge
 }