Added a geometry shader effect to the Shader example

examples/shader/Shader.cpp

@@ -258,6 +258,85 @@ private:
 };
 
 
+////////////////////////////////////////////////////////////
+// "Geometry" geometry shader example
+////////////////////////////////////////////////////////////
+class Geometry : public Effect
+{
+public:
+
+    Geometry() :
+        Effect("geometry shader billboards"),
+        m_pointCloud(sf::Points, 10000)
+    {
+    }
+
+    bool onLoad()
+    {
+        // Check if geometry shaders are supported
+        if (!sf::Shader::isGeometryAvailable())
+            return false;
+
+        // Move the points in the point cloud to random positions
+        for (std::size_t i = 0; i < 10000; i++)
+        {
+            // Spread the coordinates from -480 to +480
+            // So they'll always fill the viewport at 800x600
+            m_pointCloud[i].position.x = rand() % 960 - 480.f;
+            m_pointCloud[i].position.y = rand() % 960 - 480.f;
+        }
+
+        // Load the texture
+        if (!m_logoTexture.loadFromFile("resources/logo.png"))
+            return false;
+
+        // Load the shader
+        if (!m_shader.loadFromFile("resources/billboard.vert", "resources/billboard.geom", "resources/billboard.frag"))
+            return false;
+        m_shader.setUniform("texture", sf::Shader::CurrentTexture);
+
+        // Set the render resolution (used for proper scaling)
+        m_shader.setUniform("resolution", sf::Vector2f(800, 600));
+
+        return true;
+    }
+
+    void onUpdate(float time, float x, float y)
+    {
+        // Reset our transformation matrix
+        m_transform = sf::Transform::Identity;
+        // Move to the center of the window
+        m_transform.translate(400, 300);
+        // Rotate everything based on cursor position
+        m_transform.rotate(x * 360.f);
+
+        // Adjust billboard size to scale between 25 and 75
+        float size = 25 + std::abs(y) * 50;
+
+        // Update the shader parameter
+        m_shader.setUniform("size", sf::Vector2f(size, size));
+    }
+
+    void onDraw(sf::RenderTarget& target, sf::RenderStates states) const
+    {
+        // Prepare the render state
+        states.shader = &m_shader;
+        states.texture = &m_logoTexture;
+        states.transform = m_transform;
+
+        // Draw the point cloud
+        target.draw(m_pointCloud, states);
+    }
+
+private:
+
+    sf::Texture m_logoTexture;
+    sf::Transform m_transform;
+    sf::Shader m_shader;
+    sf::VertexArray m_pointCloud;
+};
+
+
 ////////////////////////////////////////////////////////////
 /// Entry point of application
 ///
@@ -283,6 +362,7 @@ int main()
     effects.push_back(new WaveBlur);
     effects.push_back(new StormBlink);
     effects.push_back(new Edge);
+    effects.push_back(new Geometry);
     std::size_t current = 0;
 
     // Initialize them

examples/shader/resources/billboard.frag

@@ -0,0 +1,11 @@
+#version 150
+
+uniform sampler2D texture;
+
+in vec2 tex_coord;
+
+void main()
+{
+    // Read and apply a color from the texture
+    gl_FragColor = texture2D(texture, tex_coord);
+}

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();
+    }
+}

examples/shader/resources/billboard.vert

@@ -0,0 +1,5 @@
+void main()
+{
+    // Transform the vertex position
+    gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
+}