irrlicht/media/pp_opengl.vert

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GLSL
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// Pass to fragment shader with the same name
varying vec2 TexCoords;
void main(void)
{
gl_Position = gl_Vertex;
// The origin of the texture coordinates locates at bottom-left
// corner rather than top-left corner as defined on screen quad.
// Instead of using texture coordinates passed in by OpenGL, we
// calculate TexCoords based on vertex position as follows.
//
// Vertex[0] (-1, -1) to (0, 0)
// Vertex[1] (-1, 1) to (0, 1)
// Vertex[2] ( 1, 1) to (1, 1)
// Vertex[3] ( 1, -1) to (1, 0)
//
// Texture coordinate system in OpenGL operates differently from
// DirectX 3D. It is not necessary to offset TexCoords to texel
// center by adding 1.0 / TextureSize / 2.0
TexCoords = (gl_Vertex.xy * 0.5 + 0.5);
}