Graphics Reference
In-Depth Information
We render the scene from the point of view of the light into a depth
texture using the following steps:
1.
Set up a MVP matrix using the light position.
Example 14-24 shows the MVP transformation matrix generated
by concatenating orthographic projection, model, and view
transformation matrices.
Example 14-24
Set up a MVP Matrix from the Light Position
// Generate an orthographic projection matrix
esMatrixLoadIdentity ( &ortho );
esOrtho ( &ortho, −10, 10, −10, 10, −30, 30 );
// Generate a model matrix
esMatrixLoadIdentity ( &model );
esTranslate ( &model, −2.0f, −2.0f, 0.0f );
esScale ( &model, 10.0f, 10.0f, 10.0f );
esRotate ( &model, 90.0f, 1.0f, 0.0f, 0.0f );
// Generate a view−matrix transformation
// from the light position
esMatrixLookAt ( &view,
userData−>lightPosition[0],
userData−>lightPosition[1],
userData−>lightPosition[2],
0.0f, 0.0f, 0.0f,
0.0f, 1.0f, 0.0f );
esMatrixMultiply ( &modelview, &model, &view );
// Compute the final MVP
esMatrixMultiply ( &userData−>groundMvpLightMatrix,
&modelview, &ortho );
2.
Create a depth texture and attach it to a framebuffer object.
Example 14-25 shows how to create a 1024 × 1024 16-bit depth texture
to store the shadow map. The shadow map is set with a
GL_LINEAR
texture filter. When it is used with a
sampler2Dshadow
sampler type,
we gain a hardware-based PCF, as the hardware will perform four
depth comparisons in a single tap. We then show how to render into
a framebuffer object with a depth texture attachment (recall that this
topic was discussed in Chapter 12, “Framebuffer Objects”).
