Graphics Reference
In-Depth Information
Now that we have covered the basic mathematics, we can examine the
vertex shader in Example 14-13.
Example 14-13
Projective Texturing Vertex Shader
#version 300 es
uniform float u_time_0_X;
uniform mat4 u_matProjection;
uniform mat4 u_matViewProjection;
in vec4 a_vertex;
in vec2 a_texCoord0;
in vec3 a_normal;
out vec2 v_texCoord;
out vec3 v_projTexCoord;
out vec3 v_normal;
out vec3 v_lightDir;
void main( void )
{
gl_Position = u_matViewProjection * a_vertex;
v_texCoord = a_texCoord0.xy;
// Compute a light position based on time
vec3 lightPos;
lightPos.x = cos(u_time_0_X);
lightPos.z = sin(u_time_0_X);
lightPos.xz = 200.0 * normalize(lightPos.xz);
lightPos.y = 200.0;
// Compute the light coordinate axes
vec3 look = −normalize( lightPos );
vec3 right = cross( vec3( 0.0, 0.0, 1.0), look );
vec3 up = cross( look, right );
// Create a view matrix for the light
mat4 lightView = mat4( right, dot( right, −lightPos ),
up, dot( up, −lightPos ),
look, dot( look, −lightPos),
0.0, 0.0, 0.0, 1.0 );
// Transform position into light view space
vec4 objPosLight = a_vertex * lightView;
// Transform position into projective light view space
objPosLight = u_matProjection * objPosLight;
