最简单的曲面细分着色器（Tesselation Shader）【OpenGL】【GLSL】
效果如图：
按 ‘m’ 键后
代码及详细注释如下
GLuint program;
GLuint vao;
void startup()
{
static const char * vs_source[] =
{
"#version 410 core \n"
" \n"
"void main(void) \n"
"{ \n"
" const vec4 vertices[] = vec4[](vec4( 0.25, -0.25, 0.5, 1.0), \n"
" vec4(-0.25, -0.25, 0.5, 1.0), \n"
" vec4( 0.25, 0.25, 0.5, 1.0)); \n"
" \n"
" gl_Position = vertices[gl_VertexID]; \n" // 根据当前处理的顶点 ID 为顶点位置赋值
"} \n"
};
// http://www.cnblogs.com/zenny-chen/p/4280100.html
static const char * tcs_source[] =
{
"#version 410 core \n"
" \n"
"layout (vertices = 3) out; \n" // out-patch 的顶点个数，细分控制着色器将会被执行3次
" \n"
"void main(void) \n"
"{ \n" // 仅在第一次执行（第一个顶点）时赋值（控制细分程度）
" if (gl_InvocationID == 0) \n"
" { \n"
" gl_TessLevelInner[0] = 5.0; \n" // 内部划分5个区域（新增4排顶点，见下图）
" gl_TessLevelOuter[0] = 5.0; \n" // 左边划分5段
" gl_TessLevelOuter[1] = 5.0; \n" // 右边划分5段
" gl_TessLevelOuter[2] = 5.0; \n" // 下边划分5段
" } \n"
" gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position; \n" // 通常直接将 in-patch 顶点赋给 out-patch 顶点（也可以新建或移除）
"} \n"
};
static const char * tes_source[] =
{
"#version 410 core \n"
" \n"
"layout (triangles, equal_spacing, cw) in; \n" // 指定图元生成域、细分坐标空间、图元的面朝向
//"layout (triangles, equal_spacing, cw, point_mode) in; \n" // 输出点模式
" \n"
"void main(void) \n"
"{ \n"
" gl_Position = (gl_TessCoord.x * gl_in[0].gl_Position) + \n" // gl_TessCoord：细分后的新增坐标（插值比例）
" (gl_TessCoord.y * gl_in[1].gl_Position) + \n" // 根据 input-patch 生成输出顶点的位置
" (gl_TessCoord.z * gl_in[2].gl_Position); \n" // 每个细分坐标都会让 TES 的执行一次
"} \n"
};
static const char * fs_source[] =
{
"#version 410 core \n"
" \n"
"out vec4 color; \n"
" \n"
"void main(void) \n"
"{ \n"
" color = vec4(0.0, 0.8, 1.0, 1.0); \n"
"} \n"
};
program = glCreateProgram();
GLuint vs = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vs, 1, vs_source, NULL);
glCompileShader(vs);
// Tesselation Control Shader
GLuint tcs = glCreateShader(GL_TESS_CONTROL_SHADER);
glShaderSource(tcs, 1, tcs_source, NULL);
glCompileShader(tcs);
// Tesselation Evaluation Shader
GLuint tes = glCreateShader(GL_TESS_EVALUATION_SHADER);
glShaderSource(tes, 1, tes_source, NULL);
glCompileShader(tes);
GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fs, 1, fs_source, NULL);
glCompileShader(fs);
glAttachShader(program, vs);
glAttachShader(program, tcs);
glAttachShader(program, tes);
glAttachShader(program, fs);
glLinkProgram(program);
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
}
void render()
{
static const GLfloat green[] = { 0.0f, 0.25f, 0.0f, 1.0f };
glClearBufferfv(GL_COLOR, 0, green);
glUseProgram(program);
glDrawArrays(GL_PATCHES, 0, 3);
glutSwapBuffers();
}
void shutdown()
{
glDeleteVertexArrays(1, &vao);
glDeleteProgram(program);
}
void reshape(int width, int height)
{
glViewport(0, 0, width, height);
GLfloat aspect = GLfloat(width) / height;
//glutPostRedisplay();
}
void keyboard(unsigned char key, int x, int y)
{
switch (key)
{
case 'q': case 'Q': case 033 /* Escape key */:
exit(EXIT_SUCCESS);
break;
case 'm': // 切换填充模式或镂空模式
{
static GLenum mode = GL_FILL;
mode = (mode == GL_FILL ? GL_LINE : GL_FILL);
glPolygonMode(GL_FRONT_AND_BACK, mode);
break;
}
}
glutPostRedisplay();
}
int _tmain(int argc, char* argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA /*| GLUT_STENCIL | GLUT_DEPTH*/);
glutInitWindowPosition(100, 100);
glutInitWindowSize(512, 512);
glutCreateWindow("TesselateTri"); // get an openGL context
GLenum err = glewInit(); // init glew
if (err != GLEW_OK)
{
fprintf(stderr, "Error: %s\n", glewGetErrorString(err));
exit(-2);
}
startup();
glutDisplayFunc(render);
glutReshapeFunc(reshape);
glutKeyboardFunc(keyboard);
glutMainLoop();
return 0;
}内部新增的4排顶点示意图
