/// <summary>
/// Activates the Current Vertex/Pixel shader pair into a program.
/// </summary>
private void ActivateShaderProgram()
{
// Lookup the shader program.
ShaderProgram program = programCache.GetProgram(VertexShader, PixelShader);
if (program.Program == 0)
{
return;
}
// Set the new program if it has changed.
if (shaderProgram != program)
{
GLDevice.glUseProgram(program.Program);
shaderProgram = program;
}
int posFixupLoc = shaderProgram.GetUniformLocation("posFixup");
if (posFixupLoc == -1)
{
return;
}
/* Apply vertex shader fix:
* The following two lines are appended to the end of vertex shaders
* to account for rendering differences between OpenGL and DirectX:
*
* gl_Position.y = gl_Position.y * posFixup.y;
* gl_Position.xy += posFixup.zw * gl_Position.ww;
*
* (the following paraphrased from wine, wined3d/state.c and
* wined3d/glsl_shader.c)
*
* - We need to flip along the y-axis in case of offscreen rendering.
* - D3D coordinates refer to pixel centers while GL coordinates refer
* to pixel corners.
* - D3D has a top-left filling convention. We need to maintain this
* even after the y-flip mentioned above.
*
* In order to handle the last two points, we translate by
* (63.0 / 128.0) / VPw and (63.0 / 128.0) / VPh. This is equivalent to
* translating slightly less than half a pixel. We want the difference to
* be large enough that it doesn't get lost due to rounding inside the
* driver, but small enough to prevent it from interfering with any
* anti-aliasing.
*
* OpenGL coordinates specify the center of the pixel while d3d coords
* specify the corner. The offsets are stored in z and w in posFixup.
* posFixup.y contains 1.0 or -1.0 to turn the rendering upside down for
* offscreen rendering.
*/
posFixup[0] = 1.0f;
posFixup[1] = 1.0f;
posFixup[2] = (63.0f / 64.0f) / Viewport.Width;
posFixup[3] = -(63.0f / 64.0f) / Viewport.Height;
// Flip vertically if we have a render target bound (rendering offscreen)
if (RenderTargetCount > 0)
{
posFixup[1] *= -1.0f;
posFixup[3] *= -1.0f;
}
GLDevice.glUniform4fv(
posFixupLoc,
1,
posFixupPtr
);
}