OpenGL: new built-in shaders for mesh edges

source/blender/gpu/CMakeLists.txt

@@ -157,6 +157,8 @@ data_to_c_simple(shaders/gpu_shader_2D_point_uniform_size_smooth_vert.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_2D_point_uniform_size_outline_smooth_vert.glsl SRC)
 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_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/GPU_shader.h

@@ -90,7 +90,10 @@ typedef enum GPUBuiltinShader {
 	GPU_SHADER_SMOKE             = 2,
 	GPU_SHADER_SMOKE_FIRE        = 3,
 
+	/* specialized drawing */
 	GPU_SHADER_TEXT,
+	GPU_SHADER_EDGES_FRONT_BACK_PERSP,
+	GPU_SHADER_EDGES_FRONT_BACK_ORTHO,
 
 	/* for simple 2D drawing */
 	GPU_SHADER_2D_UNIFORM_COLOR,

source/blender/gpu/intern/gpu_shader.c

@@ -77,6 +77,8 @@ extern char datatoc_gpu_shader_2D_point_uniform_size_smooth_vert_glsl[];
 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_ortho_vert_glsl[];
 extern char datatoc_gpu_shader_text_vert_glsl[];
 extern char datatoc_gpu_shader_text_frag_glsl[];
 
@@ -105,8 +107,10 @@ static struct GPUShadersGlobal {
 		GPUShader *smoke_fire;
 		/* cache for shader fx. Those can exist in combinations so store them here */
 		GPUShader *fx_shaders[MAX_FX_SHADERS * 2];
-		/* for drawing text */
+		/* specialized drawing */
 		GPUShader *text;
+		GPUShader *edges_front_back_persp;
+		GPUShader *edges_front_back_ortho;
 		/* for drawing images */
 		GPUShader *image_modulate_alpha_3D;
 		GPUShader *image_rect_modulate_alpha_3D;
@@ -656,6 +660,22 @@ GPUShader *GPU_shader_get_builtin_shader(GPUBuiltinShader shader)
 				        NULL, NULL, NULL, 0, 0, 0);
 			retval = GG.shaders.text;
 			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_frag_glsl,
+				        NULL, NULL, NULL, 0, 0, 0);
+			retval = GG.shaders.edges_front_back_persp;
+			break;
+		case GPU_SHADER_EDGES_FRONT_BACK_ORTHO:
+			if (!GG.shaders.edges_front_back_ortho)
+				GG.shaders.edges_front_back_ortho = GPU_shader_create(
+				        datatoc_gpu_shader_edges_front_back_ortho_vert_glsl,
+				        datatoc_gpu_shader_flat_color_frag_glsl,
+				        NULL, NULL, NULL, 0, 0, 0);
+			retval = GG.shaders.edges_front_back_ortho;
+			break;
 		case GPU_SHADER_3D_IMAGE_MODULATE_ALPHA:
 			if (!GG.shaders.image_modulate_alpha_3D)
 				GG.shaders.image_modulate_alpha_3D = GPU_shader_create(
@@ -938,6 +958,16 @@ void GPU_shader_free_builtin_shaders(void)
 		GG.shaders.text = NULL;
 	}
 
+	if (GG.shaders.edges_front_back_persp) {
+		GPU_shader_free(GG.shaders.edges_front_back_persp);
+		GG.shaders.edges_front_back_persp = NULL;
+	}
+
+	if (GG.shaders.edges_front_back_ortho) {
+		GPU_shader_free(GG.shaders.edges_front_back_ortho);
+		GG.shaders.edges_front_back_ortho = NULL;
+	}
+
 	if (GG.shaders.image_modulate_alpha_3D) {
 		GPU_shader_free(GG.shaders.image_modulate_alpha_3D);
 		GG.shaders.image_modulate_alpha_3D = NULL;

source/blender/gpu/shaders/gpu_shader_edges_front_back_ortho_vert.glsl

@@ -0,0 +1,64 @@
+
+// Draw "fancy" wireframe, displaying front-facing, back-facing and
+// silhouette lines differently.
+// Mike Erwin, April 2015
+
+uniform bool drawFront = true;
+uniform bool drawBack = true;
+uniform bool drawSilhouette = true;
+
+uniform vec4 frontColor;
+uniform vec4 backColor;
+uniform vec4 silhouetteColor;
+
+uniform vec4 eye; // direction we are looking
+
+uniform mat4 ModelViewProjectionMatrix;
+
+#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 both endpoints to nowhere
+// and it won't produce any fragments
+const vec4 nowhere = vec4(vec3(0.0), 1.0);
+
+void main()
+{
+	bool face_1_front = dot(N1, eye) > 0.0;
+	bool face_2_front = dot(N2, eye) > 0.0;
+
+	vec4 position = ModelViewProjectionMatrix * vec4(pos, 1.0);
+
+	if (face_1_front && face_2_front) {
+		// front-facing edge
+		gl_Position = drawFront ? position : nowhere;
+		finalColor = frontColor;
+	}
+	else if (face_1_front || face_2_front) {
+		// exactly one face is front-facing, silhouette edge
+		gl_Position = drawSilhouette ? position : nowhere;
+		finalColor = silhouetteColor;
+	}
+	else {
+		// back-facing edge
+		gl_Position = drawBack ? position : nowhere;
+		finalColor = backColor;
+	}
+}

source/blender/gpu/shaders/gpu_shader_edges_front_back_persp_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;
+	}
+}