demos/gears: Add a gears demo.

demos/gears.vert

@@ -0,0 +1,40 @@
+#version 150
+#extension GL_ARB_separate_shader_objects : enable
+
+layout(location = 0) in vec4 position_in;
+layout(location = 1) in vec3 normal_in;
+layout(location = 2) in vec3 diffuse_in;
+layout(location = 3) in vec4 transform_in;
+
+layout(location = 0) out vec4 colour_out;
+
+uniform gear_block
+{
+    uniform mat4 mvp_matrix;
+    uniform mat3 normal_matrix;
+} gear;
+
+void main()
+{
+    const vec3 l_pos = vec3(5.0, 5.0, 10.0);
+    vec3 dir, normal;
+    vec4 position;
+    float att;
+
+    position.x = transform_in.x * position_in.x - transform_in.y * position_in.y + transform_in.z;
+    position.y = transform_in.x * position_in.y + transform_in.y * position_in.x + transform_in.w;
+    position.zw = position_in.zw;
+
+    gl_Position = gear.mvp_matrix * position;
+    dir = normalize(l_pos - gl_Position.xyz / gl_Position.w);
+
+    normal.x = transform_in.x * normal_in.x - transform_in.y * normal_in.y;
+    normal.y = transform_in.x * normal_in.y + transform_in.y * normal_in.x;
+    normal.z = normal_in.z;
+    att = 0.2 + dot(dir, normalize(gear.normal_matrix * normal));
+
+    colour_out.xyz = diffuse_in.xyz * att;
+    colour_out.w = 1.0;
+
+    gl_Position.y = -gl_Position.y;
+}