Graphics Reference
In-Depth Information
Example 8-6
Vertex Skinning Shader with No Check of Whether
Matrix Weight = 0
(continued)
m_wt = a_matrixweights[3];
m_indx = int ( a_matrixindices[3] ) * c_three;
skin_position ( position, m_wt, m_indx, skinned_position );
skin_normal ( normal, m_wt, m_indx, skinned_normal );
}
// add a main function to make this into a valid vertex shader
In Example 8-6, the vertex skinning shader generates a skinned vertex by
transforming a vertex with four matrices and appropriate matrix weights.
It is possible and quite common that some of these matrix weights
may be zero. In Example 8-6, the vertex is transformed using all four
matrices, irrespective of their weights. It might be better, however, to use a
conditional expression to check whether the matrix weight is zero before
calling
skin_position
and
skin_normal
. In Example 8-7, the vertex
skinning shader checks for a matrix weight of zero before applying the
matrix transformation.
Example 8-7
Vertex Skinning Shader with Checks of Whether
Matrix Weight = 0
void do_skinning ( in vec4 position, in vec3 normal,
out vec4 skinned_position,
out vec3 skinned_normal )
{
skinned_position = vec4 ( float ( c_zero ) );
skinned_normal = vec3 ( float( c_zero ) );
// transform position and normal to eye space using matrix
// palette with four matrices used to transform a vertex
int m_indx = 0;
float m_wt = a_matrixweights[0];
if ( m_wt > 0.0 )
{
m_indx = int ( a_matrixindices[0] ) * c_three;
skin_position( position, m_wt, m_indx, skinned_position );
skin_normal ( normal, m_wt, m_indx, skinned_normal );
}
m_wt = a_matrixweights[1] ;
if ( m_wt > 0.0 )
