1 files changed, 70 insertions, 2 deletions

diff --git a/source/blender/draw/modes/shaders/paint_weight_frag.glsl b/source/blender/draw/modes/shaders/paint_weight_frag.glsl
index bb0834e9cd4..faa36f5535e 100644
--- a/source/blender/draw/modes/shaders/paint_weight_frag.glsl
+++ b/source/blender/draw/modes/shaders/paint_weight_frag.glsl
@@ -6,13 +6,71 @@ out vec4 fragColor;
 uniform float opacity = 1.0;
 uniform sampler1D colorramp;
 
+uniform bool drawContours = false;
+
+float contours(float value, float steps, float width_px, float max_rel_width, float gradient)
+{
+	/* Minimum visible and minimum full strength line width in screen space for fade out. */
+	const float min_width_px = 1.3, fade_width_px = 2.3;
+	/* Line is thinner towards the increase in the weight gradient by this factor. */
+	const float hi_bias = 2.0;
+
+	/* Don't draw lines at 0 or 1. */
+	float rel_value = value * steps;
+
+	if (rel_value < 0.5 || rel_value > steps - 0.5)
+		return 0.0;
+
+	/* Check if completely invisible due to fade out. */
+	float rel_gradient = gradient * steps;
+	float rel_min_width = min_width_px * rel_gradient;
+
+	if (max_rel_width <= rel_min_width)
+		return 0.0;
+
+	/* Main shape of the line, accounting for width bias and maximum weight space width. */
+	float rel_width = width_px * rel_gradient;
+
+	float offset = fract(rel_value + 0.5) - 0.5;
+
+	float base_alpha = 1.0 - max(offset * hi_bias, -offset) / min(max_rel_width, rel_width);
+
+	/* Line fadeout when too thin in screen space. */
+	float rel_fade_width = fade_width_px * rel_gradient;
+
+	float fade_alpha = (max_rel_width - rel_min_width) / (rel_fade_width - rel_min_width);
+
+	return clamp(base_alpha, 0.0, 1.0) * clamp(fade_alpha, 0.0, 1.0);
+}
+
+vec4 contour_grid(float weight, float weight_gradient)
+{
+	/* Fade away when the gradient is too low to avoid big fills and noise. */
+	float flt_eps = max(1e-8, 1e-6 * weight);
+
+	if (weight_gradient <= flt_eps)
+		return vec4(0.0);
+
+	/* Three levels of grid lines */
+	float grid10 = contours(weight, 10.0, 5.0, 0.3, weight_gradient);
+	float grid100 = contours(weight, 100.0, 3.5, 0.35, weight_gradient) * 0.6;
+	float grid1000 = contours(weight, 1000.0, 2.5, 0.4, weight_gradient) * 0.25;
+
+	/* White lines for 0.1 and 0.01, and black for 0.001 */
+	vec4 grid = vec4(1.0) * max(grid10, grid100);
+
+	grid.a = max(grid.a, grid1000);
+
+	return grid * clamp((weight_gradient - flt_eps) / flt_eps, 0.0, 1.0);
+}
+
 void main()
 {
 	float alert = weight_interp.y;
 	vec4 color;
 
-	/* Missing vertex group alert color */
-	if (alert > 1.0) {
+	/* Missing vertex group alert color. Uniform in practice. */
+	if (alert > 1.1) {
 		color = colorVertexMissingData;
 	}
 	/* Weights are available */
@@ -20,6 +78,16 @@ void main()
 		float weight = weight_interp.x;
 		vec4 weight_color = texture(colorramp, weight, 0);
 
+		/* Contour display */
+		if (drawContours) {
+			/* This must be executed uniformly for all fragments */
+			float weight_gradient = length(vec2(dFdx(weight), dFdy(weight)));
+
+			vec4 grid = contour_grid(weight, weight_gradient);
+
+			weight_color = grid + weight_color * (1 - grid.a);
+		}
+
 		/* Zero weight alert color. Nonlinear blend to reduce impact. */
 		color = mix(weight_color, colorVertexUnreferenced, alert * alert);
 	}