Overlay: Add Wireframe overlay.

This overlay is showing mesh topology. It is usable with transparency
even if the mesh order can mess up with the expected result (some object
more prominent than others).

Edge thickness and alpha values are hardcoded for now but can easily be
added to theme or object settings.

1 files changed, 36 insertions, 0 deletions

diff --git a/source/blender/draw/modes/shaders/overlay_face_wireframe_frag.glsl b/source/blender/draw/modes/shaders/overlay_face_wireframe_frag.glsl
new file mode 100644
index 00000000000..86e3bb959e9
--- /dev/null
+++ b/source/blender/draw/modes/shaders/overlay_face_wireframe_frag.glsl
@@ -0,0 +1,36 @@
+uniform vec3 wireColor;
+uniform vec3 rimColor;
+
+flat in vec3 ssVec0;
+flat in vec3 ssVec1;
+flat in vec3 ssVec2;
+in float facing;
+
+out vec4 fragColor;
+
+float min_v3(vec3 v) { return min(v.x, min(v.y, v.z)); }
+
+/* In pixels */
+const float wire_size = 0.0; /* Expands the core of the wire (part that is 100% wire color) */
+const float wire_smooth = 1.4; /* Smoothing distance after the 100% core. */
+
+/* Alpha constants could be exposed in the future. */
+const float front_alpha = 0.55;
+const float rim_alpha = 0.75;
+
+void main()
+{
+	vec3 ss_pos = vec3(gl_FragCoord.xy, 1.0);
+	vec3 dist_to_edge = vec3(
+		dot(ss_pos, ssVec0),
+		dot(ss_pos, ssVec1),
+		dot(ss_pos, ssVec2)
+	);
+
+	float fac = smoothstep(wire_size, wire_size + wire_smooth, min_v3(abs(dist_to_edge)));
+	float facing_clamped = clamp((gl_FrontFacing) ? facing : -facing, 0.0, 1.0);
+
+	vec3 final_front_col = rimColor * 0.5 + wireColor * 0.5;
+	fragColor = mix(vec4(rimColor, rim_alpha), vec4(final_front_col, front_alpha), facing_clamped);
+	fragColor.a *= (1.0 - fac);
+}