first commit

addons/zylann.hterrain/tools/brush/shaders/erode.gdshader

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+shader_type canvas_item;
+render_mode blend_disabled;
+
+#include "res://addons/zylann.hterrain/shaders/include/heightmap.gdshaderinc"
+
+uniform sampler2D u_src_texture;
+uniform vec4 u_src_rect;
+uniform float u_opacity = 1.0;
+uniform vec4 u_color = vec4(1.0);
+
+vec2 get_src_uv(vec2 screen_uv) {
+	vec2 uv = u_src_rect.xy + screen_uv * u_src_rect.zw;
+	return uv;
+}
+
+// float get_noise(vec2 pos) {
+// 	return fract(sin(dot(pos.xy ,vec2(12.9898,78.233))) * 43758.5453);
+// }
+
+float get_height(sampler2D heightmap, vec2 uv) {
+	return sample_heightmap(heightmap, uv);
+}
+
+float erode(sampler2D heightmap, vec2 uv, vec2 pixel_size, float weight) {
+	float r = 3.0;
+	
+	// Divide so the shader stays neighbor dependent 1 pixel across.
+	// For this to work, filtering must be enabled.
+	vec2 eps = pixel_size / (0.99 * r);
+	
+	float h = get_height(heightmap, uv);
+	float eh = h;
+	//float dh = h;
+	
+	// Morphology with circular structuring element
+	for (float y = -r; y <= r; ++y) {
+		for (float x = -r; x <= r; ++x) {
+			
+			vec2 p = vec2(x, y);
+			float nh = get_height(heightmap, uv + p * eps);
+			
+			float s = max(length(p) - r, 0);
+			eh = min(eh, nh + s);
+
+			//s = min(r - length(p), 0);
+			//dh = max(dh, nh + s);
+		}
+	}
+	
+	eh = mix(h, eh, weight);
+	//dh = mix(h, dh, u_weight);
+	
+	float ph = eh;//mix(eh, dh, u_dilation);
+
+	return ph;
+}
+
+void fragment() {
+	float brush_value = u_opacity * texture(TEXTURE, UV).r;
+	vec2 src_pixel_size = 1.0 / vec2(textureSize(u_src_texture, 0));
+	float ph = erode(u_src_texture, get_src_uv(SCREEN_UV), src_pixel_size, brush_value);
+	//ph += brush_value * 0.35;
+	COLOR = encode_height_to_viewport(ph);
+}