这里只提一种最基本的混合,其他的混合方式可以参考书中的表格
混合代码如下:
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vRed);
squareBatch.Draw();
glDisable(GL_BLEND);
大部分代码前面我们都已经接触过,主要解释一下glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
最终显示的颜色为 源颜色的alpha * 源颜色 + 目标颜色的颜色*(1-alpha)
如下图所示:
完整代码如下:
#include <GLTools.h> // OpenGL toolkit
#define FREEGLUT_STATIC //在windows和linux上,使用freeglut静态版本,需要添加这一行,否则会出现错误
#include <glut.h>
#pragma comment(lib,"gltools.lib")//要加上这一行链接一下gltools库
GLBatch squareBatch;
GLBatch greenBatch;
GLBatch redBatch;
GLBatch blueBatch;
GLBatch blackBatch;
GLShaderManager shaderManager;
GLfloat blockSize = 0.2f;
GLfloat vVerts[] = { -blockSize, -blockSize, 0.0f,
blockSize, -blockSize, 0.0f,
blockSize, blockSize, 0.0f,
-blockSize, blockSize, 0.0f };
void SetupRC()
{
glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
shaderManager.InitializeStockShaders();
// Load up a triangle fan
squareBatch.Begin(GL_TRIANGLE_FAN, 4);
squareBatch.CopyVertexData3f(vVerts);
squareBatch.End();
GLfloat vBlock[] = { 0.25f, 0.25f, 0.0f,
0.75f, 0.25f, 0.0f,
0.75f, 0.75f, 0.0f,
0.25f, 0.75f, 0.0f };
greenBatch.Begin(GL_TRIANGLE_FAN, 4);
greenBatch.CopyVertexData3f(vBlock);
greenBatch.End();
GLfloat vBlock2[] = { -0.75f, 0.25f, 0.0f,
-0.25f, 0.25f, 0.0f,
-0.25f, 0.75f, 0.0f,
-0.75f, 0.75f, 0.0f };
redBatch.Begin(GL_TRIANGLE_FAN, 4);
redBatch.CopyVertexData3f(vBlock2);
redBatch.End();
GLfloat vBlock3[] = { -0.75f, -0.75f, 0.0f,
-0.25f, -0.75f, 0.0f,
-0.25f, -0.25f, 0.0f,
-0.75f, -0.25f, 0.0f };
blueBatch.Begin(GL_TRIANGLE_FAN, 4);
blueBatch.CopyVertexData3f(vBlock3);
blueBatch.End();
GLfloat vBlock4[] = { 0.25f, -0.75f, 0.0f,
0.75f, -0.75f, 0.0f,
0.75f, -0.25f, 0.0f,
0.25f, -0.25f, 0.0f };
blackBatch.Begin(GL_TRIANGLE_FAN, 4);
blackBatch.CopyVertexData3f(vBlock4);
blackBatch.End();
}
// Respond to arrow keys by moving the camera frame of reference
void SpecialKeys(int key, int x, int y)
{
GLfloat stepSize = 0.025f;
GLfloat blockX = vVerts[0]; // Upper left X
GLfloat blockY = vVerts[7]; // Upper left Y
if (key == GLUT_KEY_UP)
blockY += stepSize;
if (key == GLUT_KEY_DOWN)
blockY -= stepSize;
if (key == GLUT_KEY_LEFT)
blockX -= stepSize;
if (key == GLUT_KEY_RIGHT)
blockX += stepSize;
// Collision detection
if (blockX < -1.0f) blockX = -1.0f;
if (blockX >(1.0f - blockSize * 2)) blockX = 1.0f - blockSize * 2;;
if (blockY < -1.0f + blockSize * 2) blockY = -1.0f + blockSize * 2;
if (blockY > 1.0f) blockY = 1.0f;
// Recalculate vertex positions
vVerts[0] = blockX;
vVerts[1] = blockY - blockSize * 2;
vVerts[3] = blockX + blockSize * 2;
vVerts[4] = blockY - blockSize * 2;
vVerts[6] = blockX + blockSize * 2;
vVerts[7] = blockY;
vVerts[9] = blockX;
vVerts[10] = blockY;
squareBatch.CopyVertexData3f(vVerts);
glutPostRedisplay();
}
///////////////////////////////////////////////////////////////////////////////
// Called to draw scene
void RenderScene(void)
{
// Clear the window with current clearing color
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
GLfloat vRed[] = { 1.0f, 0.0f, 0.0f, 0.5f };
GLfloat vGreen[] = { 0.0f, 1.0f, 0.0f, 1.0f };
GLfloat vBlue[] = { 0.0f, 0.0f, 1.0f, 1.0f };
GLfloat vBlack[] = { 0.0f, 0.0f, 0.0f, 1.0f };
shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vGreen);
greenBatch.Draw();
shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vRed);
redBatch.Draw();
shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vBlue);
blueBatch.Draw();
shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vBlack);
blackBatch.Draw();
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vRed);
squareBatch.Draw();
glDisable(GL_BLEND);
// Flush drawing commands
glutSwapBuffers();
}
void ChangeSize(int w, int h)
{
glViewport(0, 0, w, h);
}
int main(int argc, char* argv[])
{
gltSetWorkingDirectory(argv[0]);
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);
glutInitWindowSize(800, 600);
glutCreateWindow("Move Block with Arrow Keys to see blending");
GLenum err = glewInit();
if (GLEW_OK != err)
{
fprintf(stderr, "Error: %s\n", glewGetErrorString(err));
return 1;
}
glutReshapeFunc(ChangeSize);
glutDisplayFunc(RenderScene);
glutSpecialFunc(SpecialKeys);
SetupRC();
glutMainLoop();
return 0;
}