Added a geometry shader effect to the Shader example

examples/shader/resources/billboard.geom

@@ -0,0 +1,56 @@
+#version 150
+
+// The render target's resolution (used for scaling)
+uniform vec2 resolution;
+
+// The billboards' size
+uniform vec2 size;
+
+// Input is the passed point cloud
+layout (points) in;
+
+// The output will consist of triangle strips with four vertices each
+layout (triangle_strip, max_vertices = 4) out;
+
+// Output texture coordinates
+out vec2 tex_coord;
+
+// Main entry point
+void main()
+{
+    // Caculate the half width/height of the billboards
+    vec2 half_size = size / 2.f;
+
+    // Scale the size based on resolution (1 would be full width/height)
+    half_size /= resolution;
+
+    // Iterate over all vertices
+    for (int i = 0; i < gl_in.length(); i++)
+    {
+        // Retrieve the passed vertex position
+        vec2 pos = gl_in[i].gl_Position.xy;
+
+        // Bottom left vertex
+        gl_Position = vec4(pos - half_size, 0.f, 1.f);
+        tex_coord = vec2(1.f, 1.f);
+        EmitVertex();
+
+        // Bottom right vertex
+        gl_Position = vec4(pos.x + half_size.x, pos.y - half_size.y, 0.f, 1.f);
+        tex_coord = vec2(0.f, 1.f);
+        EmitVertex();
+
+        // Top left vertex
+        gl_Position = vec4(pos.x - half_size.x, pos.y + half_size.y, 0.f, 1.f);
+        tex_coord = vec2(1.f, 0.f);
+        EmitVertex();
+
+        // Top right vertex
+        gl_Position = vec4(pos + half_size, 0.f, 1.f);
+        tex_coord = vec2(0.f, 0.f);
+        EmitVertex();
+
+        // And finalize the primitive
+        EndPrimitive();
+    }
+}