Armature: "Raytrace" bones endpoint spheres.

Here is how it works:
We render a high poly disc that we orient & scale towards the camera so that
it covers the same pixel of the sphere it's supposed to represent.

Then the pixel shader raytrace the sphere (effectively starting from
the poly disc depth) and outputs the depth to gl_FragDepth.

This approach has many benefit:
- high quality obviously: per pixel accurate depth!
- compatible with MSAA: since the sphere horizon is delimited by polygons,
  we get the coverage computed by the rasterizer. However we still gets
  aliasing if the sphere intersect directly other meshes.
- virtually no overdraw: there is no backface to shade but we still get
  overdraw because by little triangle [gpus rasterize pixel by groups of 4].
- allows early depth test: since the poly disc is set at the nearest depth
  we can output, we can use GL_ARB_conservative_depth to enable early depth
  test and discard pixels that are already behind geometry.
- can draw outline pretty easily without geometry shader.

1 files changed, 46 insertions, 0 deletions

diff --git a/source/blender/draw/intern/draw_common.c b/source/blender/draw/intern/draw_common.c
index 3a2aa970a9b..6d684b1c9fb 100644
--- a/source/blender/draw/intern/draw_common.c
+++ b/source/blender/draw/intern/draw_common.c
@@ -156,12 +156,17 @@ void DRW_globals_update(void)
 
 /* ********************************* SHGROUP ************************************* */
 
+extern char datatoc_armature_sphere_vert_glsl[];
+extern char datatoc_armature_sphere_frag_glsl[];
+extern char datatoc_armature_sphere_outline_vert_glsl[];
 extern char datatoc_armature_shape_outline_vert_glsl[];
 extern char datatoc_armature_shape_outline_geom_glsl[];
 extern char datatoc_gpu_shader_flat_color_frag_glsl[];
 
 static struct {
 	struct GPUShader *shape_outline;
+	struct GPUShader *bone_sphere;
+	struct GPUShader *bone_sphere_outline;
 } g_armature_shaders = {NULL};
 
 static struct {
@@ -491,6 +496,47 @@ DRWShadingGroup *shgroup_instance_armature_shape_outline(DRWPass *pass, struct G
 	return grp;
 }
 
+DRWShadingGroup *shgroup_instance_armature_sphere(DRWPass *pass)
+{
+	if (g_armature_shaders.bone_sphere == NULL) {
+		g_armature_shaders.bone_sphere = DRW_shader_create(
+		            datatoc_armature_sphere_vert_glsl, NULL,
+		            datatoc_armature_sphere_frag_glsl, NULL);
+	}
+
+	/* TODO own format? */
+	DRW_shgroup_instance_format(g_formats.instance_color, {
+		{"InstanceModelMatrix", DRW_ATTRIB_FLOAT, 16},
+		{"color"              , DRW_ATTRIB_FLOAT, 4}
+	});
+
+	DRWShadingGroup *grp = DRW_shgroup_instance_create(g_armature_shaders.bone_sphere,
+	                                                   pass, DRW_cache_bone_point_get(), g_formats.instance_color);
+
+	return grp;
+}
+
+DRWShadingGroup *shgroup_instance_armature_sphere_outline(DRWPass *pass)
+{
+	if (g_armature_shaders.bone_sphere_outline == NULL) {
+		g_armature_shaders.bone_sphere_outline = DRW_shader_create(
+		            datatoc_armature_sphere_outline_vert_glsl, NULL,
+		            datatoc_gpu_shader_flat_color_frag_glsl, NULL);
+	}
+
+	/* TODO own format? */
+	DRW_shgroup_instance_format(g_formats.instance_color, {
+		{"InstanceModelMatrix", DRW_ATTRIB_FLOAT, 16},
+		{"color"              , DRW_ATTRIB_FLOAT, 4}
+	});
+
+	DRWShadingGroup *grp = DRW_shgroup_instance_create(g_armature_shaders.bone_sphere_outline,
+	                                                   pass, DRW_cache_bone_point_wire_outline_get(),
+	                                                   g_formats.instance_color);
+	DRW_shgroup_uniform_vec2(grp, "viewportSize", DRW_viewport_size_get(), 1);
+
+	return grp;
+}