Workbench: Xray: Make nearest surfaces more clear

By using equation 7 from the paper, we make the surfaces nearest to the
viewpoint appear more "opaque". This gives better sense of ordering than
the previous weighting function that was really not doing anything.

3 files changed, 34 insertions, 6 deletions

diff --git a/source/blender/draw/engines/workbench/shaders/workbench_common_lib.glsl b/source/blender/draw/engines/workbench/shaders/workbench_common_lib.glsl
index 0b494aa019f..c56e02e72d6 100644
--- a/source/blender/draw/engines/workbench/shaders/workbench_common_lib.glsl
+++ b/source/blender/draw/engines/workbench/shaders/workbench_common_lib.glsl
@@ -65,11 +65,38 @@ void fresnel(vec3 I, vec3 N, float ior, out float kr)
 	// kt = 1 - kr;
 }
 
-float calculate_transparent_weight(float alpha) {
-	/* Eq 10 */
-	float a = min(1.0, alpha) * 8.0 + 0.01;
+float calculate_transparent_weight(float z, float alpha)
+{
+#if 0
+	/* Eq 10 : Good for surfaces with varying opacity (like particles) */
+	float a = min(1.0, alpha * 10.0) + 0.01;
 	float b = -gl_FragCoord.z * 0.95 + 1.0;
-	return alpha * clamp(a * a * a * 1e8 * b * b * b, 1e-2, 3e3);
+	float w = a * a * a * 3e2 * b * b * b;
+#else
+	/* Eq 7 put more emphasis on surfaces closer to the view. */
+	// float w = 10.0 / (1e-5 + pow(abs(z) / 5.0, 2.0) + pow(abs(z) / 200.0, 6.0)); /* Eq 7 */
+	// float w = 10.0 / (1e-5 + pow(abs(z) / 10.0, 3.0) + pow(abs(z) / 200.0, 6.0)); /* Eq 8 */
+	// float w = 10.0 / (1e-5 + pow(abs(z) / 200.0, 4.0)); /* Eq 9 */
+	/* Same as eq 7, but optimized. */
+	float a = abs(z) / 5.0;
+	float b = abs(z) / 200.0;
+	b *= b;
+	float w = 10.0 / ((1e-5 + a * a) + b * (b * b)); /* Eq 7 */
+#endif
+	return alpha * clamp(w, 1e-2, 3e2);
+}
+
+/* Special function only to be used with calculate_transparent_weight(). */
+float linear_zdepth(float depth, vec4 viewvecs[3], mat4 proj_mat)
+{
+	if (proj_mat[3][3] == 0.0) {
+		float d = 2.0 * depth - 1.0;
+		return -proj_mat[3][2] / (d + proj_mat[2][2]);
+	}
+	else {
+		/* Return depth from near plane. */
+		return depth * viewvecs[1].z;
+	}
 }
 
 vec3 view_vector_from_screen_uv(vec2 uv, vec4 viewvecs[3], mat4 proj_mat)
diff --git a/source/blender/draw/engines/workbench/shaders/workbench_forward_transparent_accum_frag.glsl b/source/blender/draw/engines/workbench/shaders/workbench_forward_transparent_accum_frag.glsl
index 53903a4af76..4a7d195a56a 100644
--- a/source/blender/draw/engines/workbench/shaders/workbench_forward_transparent_accum_frag.glsl
+++ b/source/blender/draw/engines/workbench/shaders/workbench_forward_transparent_accum_frag.glsl
@@ -75,7 +75,8 @@ void main()
 	 * Computer Graphics Techniques (JCGT), vol. 2, no. 2, 122–141, 2013
 	 */
 	/* Listing 4 */
-	float weight = calculate_transparent_weight(alpha);
+	float z = linear_zdepth(gl_FragCoord.z, viewvecs, ProjectionMatrix);
+	float weight = calculate_transparent_weight(z, alpha);
 	transparentAccum = vec4(shaded_color * weight, alpha);
 	revealageAccum = weight;
 }
diff --git a/source/blender/draw/engines/workbench/workbench_forward.c b/source/blender/draw/engines/workbench/workbench_forward.c
index fb949cd02c9..4e97fc730a3 100644
--- a/source/blender/draw/engines/workbench/workbench_forward.c
+++ b/source/blender/draw/engines/workbench/workbench_forward.c
@@ -172,6 +172,7 @@ static WORKBENCH_MaterialData *get_or_create_material_data(
 		        psl->transparent_accum_pass);
 		DRW_shgroup_uniform_block(grp, "world_block", wpd->world_ubo);
 		DRW_shgroup_uniform_float(grp, "alpha", &wpd->shading.xray_alpha, 1);
+		DRW_shgroup_uniform_vec4(grp, "viewvecs[0]", (float *)wpd->viewvecs, 3);
 		workbench_material_set_normal_world_matrix(grp, wpd, e_data.normal_world_matrix);
 		material->object_id = engine_object_data->object_id;
 		copy_v4_v4(material->material_data.diffuse_color, material_template.material_data.diffuse_color);
@@ -185,7 +186,6 @@ static WORKBENCH_MaterialData *get_or_create_material_data(
 					DRW_shgroup_uniform_texture(grp, "matcapImage", wpd->studio_light->equirectangular_radiance_gputexture);
 				}
 				if (SPECULAR_HIGHLIGHT_ENABLED(wpd) || MATCAP_ENABLED(wpd)) {
-					DRW_shgroup_uniform_vec4(grp, "viewvecs[0]", (float *)wpd->viewvecs, 3);
 					DRW_shgroup_uniform_vec2(grp, "invertedViewportSize", DRW_viewport_invert_size_get(), 1);
 				}
 				break;