[计算机软件及应用]OpenGL ES 2O知识总结.pdfVIP

Figure 1-1 OpenGL ES 2.0 Graphics Pipeline Vertex Shader Figure 1-2 OpenGL ES 2.0 Vertex Shader The vertex shader implements a general purpose programmable method for operating on vertices. The inputs to the vertex （顶点） shader （背阴） consist of the following: • Attributes—Per-vertex data supplied using vertex arrays. • Uniforms—Constant data used by the vertex shader. • Samplers—A specific type of uniforms that represent textures used by the vertex shader. Samplers in a vertex shader are optional. • Shader program—Vertex shader program source code or executable that describes the operations that will be performed on the vertex. Vertex shaders can be used for traditional vertex-based operations such as transforming the position by a matrix, computing the lighting equation to generate a per-vertex color, and generating or transforming texture coordi- nates. Alternately, because the vertex shader is specified by the application, vertex shaders can be used to do custom vertex transformations. Example 1-1 A Vertex Shader Example 1. // uniforms （统⼀） used by the vertex shader 2. uniform mat4 u_mvpMatrix; // matrix to convert P from model 3. // space to normalized device space. 4. 5. // attributes input to the vertex shader 6. attribute vec4 a_position; // position value 7. attribute vec4 a_color; // input vertex color 8. 9. // varying variables – input to the fragment shader 10. varying vec4 v_color; // output vertex color 11. 12. void 13. main() 14. { 15. v_color = a_color; 16. gl_Position = u_mvpMatrix * a_position; 17. } The vertex shader in Example 1-1 takes a position and its associ-ated （链接） color data as input attributes, transforms the position by a 4 × 4 matrix and outputs the transformed position and color. Line 2 describes a uniform variable u_mvpMatrix that stores the combined model view and projection matrix. Lines 6 and 7 describe the inputs to the vertex s