Use renderpass to render layers above ghosts

CURA-1601

plugins/LayerView/layerview_composite.shader

@@ -0,0 +1,80 @@
+[shaders]
+vertex =
+    uniform highp mat4 u_modelViewProjectionMatrix;
+    attribute highp vec4 a_vertex;
+    attribute highp vec2 a_uvs;
+
+    varying highp vec2 v_uvs;
+
+    void main()
+    {
+        gl_Position = u_modelViewProjectionMatrix * a_vertex;
+        v_uvs = a_uvs;
+    }
+
+fragment =
+    uniform sampler2D u_layer0;
+    uniform sampler2D u_layer1;
+    uniform sampler2D u_layer2;
+    uniform sampler2D u_layer3;
+
+    uniform float u_imageWidth;
+    uniform float u_imageHeight;
+
+    uniform vec2 u_offset[9];
+
+    uniform float u_outline_strength;
+    uniform vec4 u_outline_color;
+
+    varying vec2 v_uvs;
+
+    float kernel[9];
+
+    const vec3 x_axis = vec3(1.0, 0.0, 0.0);
+    const vec3 y_axis = vec3(0.0, 1.0, 0.0);
+    const vec3 z_axis = vec3(0.0, 0.0, 1.0);
+
+    void main()
+    {
+        kernel[0] = 0.0; kernel[1] = 1.0; kernel[2] = 0.0;
+        kernel[3] = 1.0; kernel[4] = -4.0; kernel[5] = 1.0;
+        kernel[6] = 0.0; kernel[7] = 1.0; kernel[8] = 0.0;
+
+        vec4 result = vec4(0.965, 0.965, 0.965, 1.0);
+        vec4 layer0 = texture2D(u_layer0, v_uvs);
+        vec4 layer2 = texture2D(u_layer2, v_uvs);
+
+        result = layer0 * layer0.a + result * (1.0 - layer0.a);
+        result = layer2 * layer2.a + result * (1.0 - layer2.a);
+
+        vec4 sum = vec4(0.0);
+        for (int i = 0; i < 9; i++)
+        {
+            vec4 color = vec4(texture2D(u_layer1, v_uvs.xy + u_offset[i]).a);
+            sum += color * (kernel[i] / u_outline_strength);
+        }
+
+        vec4 layer1 = texture2D(u_layer1, v_uvs);
+        if((layer1.rgb == x_axis || layer1.rgb == y_axis || layer1.rgb == z_axis))
+        {
+            gl_FragColor = result;
+        }
+        else
+        {
+            gl_FragColor = mix(result, u_outline_color, abs(sum.a));
+        }
+    }
+
+[defaults]
+u_layer0 = 0
+u_layer1 = 1
+u_layer2 = 2
+u_layer3 = 3
+u_outline_strength = 1.0
+u_outline_color = [0.05, 0.66, 0.89, 1.0]
+
+[bindings]
+
+[attributes]
+a_vertex = vertex
+a_uvs = uv