[ui] Viewer3D: introduce SphericalHarmonics shader + display mode

Add experimental render mode to display model normals or shading based on spherical harmonics coefficients

meshroom/ui/qml/Viewer3D/Materials/shaders/SphericalHarmonics.frag

@@ -0,0 +1,34 @@
+#version 330 core
+
+in vec3 normal;
+out vec4 fragColor;
+
+uniform vec3 shCoeffs[9];
+uniform bool displayNormals = false;
+
+vec3 resolveSH_Opt(vec3 premulCoefficients[9], vec3 dir)
+{
+    vec3 result = premulCoefficients[0] * dir.x;
+    result += premulCoefficients[1] * dir.y;
+    result += premulCoefficients[2] * dir.z;
+    result += premulCoefficients[3];
+    vec3 dirSq = dir * dir;
+    result += premulCoefficients[4] * (dir.x * dir.y);
+    result += premulCoefficients[5] * (dir.x * dir.z);
+    result += premulCoefficients[6] * (dir.y * dir.z);
+    result += premulCoefficients[7] * (dirSq.x - dirSq.y);
+    result += premulCoefficients[8] * (3 * dirSq.z - 1);
+    return result;
+}
+
+void main()
+{
+    if(displayNormals) {
+        // Display normals mode
+        fragColor = vec4(normal, 1.0);
+    }
+    else {
+        // Calculate the color from spherical harmonics coeffs
+        fragColor = vec4(resolveSH_Opt(shCoeffs, normal), 1.0);
+    }
+}

meshroom/ui/qml/Viewer3D/Materials/shaders/SphericalHarmonics.vert

@@ -0,0 +1,16 @@
+#version 330 core
+
+in vec3 vertexPosition;
+in vec3 vertexNormal;
+
+out vec3 normal;
+
+uniform mat4 modelView;
+uniform mat3 modelViewNormal;
+uniform mat4 mvp;
+
+void main()
+{
+    normal = vertexNormal;
+    gl_Position = mvp * vec4( vertexPosition, 1.0 );
+}