OpenGL代码学习（10）--颜色混合

注意：需要在配置好OpenGL的编程环境中运行下列代码，环境配置文章可参考：

OpenGL在Mac项目上的配置

下面的代码，直接放置在main.cpp文件中即可：

#include "GLTools.h"
#include "GLShaderManager.h"
#include <GLUT/GLUT.h>

GLBatch squareBatch;
GLBatch greenBatch;
GLBatch redBatch;
GLBatch blueBatch;
GLBatch blackBatch;

GLShaderManager shaderManager;

GLfloat blockSize = 0.5f;
GLfloat vVerts[] = {
    -blockSize, -blockSize, 0.0f,
    blockSize, -blockSize, 0.0f,
    blockSize, blockSize, 0.0f,
    -blockSize, blockSize, 0.0f
};

// 程序一次性初始化
void SetupRC() {
    // 设置窗口背景为黑色
    glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
    // 初始化着色器管理者
    shaderManager.InitializeStockShaders();
    
    // 创建移动矩形批次
    squareBatch.Begin(GL_TRIANGLE_FAN, 4);
    squareBatch.CopyVertexData3f(vVerts);
    squareBatch.End();
    
    // 绿色矩形批次
    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();
    
    // 红色矩形批次
    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();
    
    // 蓝色矩形批次
    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();
    
    // 黑色矩形批次
    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();
}

// 特殊按键监听
void SpecialKeys(int key, int x, int y) {
    GLfloat stepSize = 0.025f;
    // 左上角的x坐标和右下角的y坐标
    GLfloat blockX = vVerts[0];
    GLfloat blockY = vVerts[7];
    
    // 根据移动方向移动位置
    switch (key) {
        case GLUT_KEY_UP:
            blockY += stepSize;
            break;
        case GLUT_KEY_DOWN:
            blockY -= stepSize;
            break;
        case GLUT_KEY_LEFT:
            blockX -= stepSize;
            break;
        case GLUT_KEY_RIGHT:
            blockX += stepSize;
            break;
        default:
            break;
    }
    
    // 移动边界处理
    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;
    }
    
    // 矩形四个顶点位置
    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;
    
    // 批次顶点数据编号
    squareBatch.CopyVertexData3f(vVerts);
    
    // 触发渲染
    glutPostRedisplay();
}

// 渲染画面
void RenderScene(void) {
    // 清理各个缓存区
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
    
    // 定义4种颜色
    GLfloat vRed[] = {1.0f, 0.0f, 0.0f, 1.0f};
    GLfloat vGreen[] = {0.0f, 1.0f, 0.0f, 1.0f};
    GLfloat vBlue[] = {0.0f, 0.0f, 1.0f, 0.6f};
    GLfloat vBlack[] = {0.0f, 0.0f, 0.0f, 1.0f};
    
    // 画绿色矩形
    shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vGreen);
    greenBatch.Draw();
    
    // 画红色矩形
    shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vRed);
    redBatch.Draw();
    
    // 画蓝色矩形
    shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vBlue);
    blueBatch.Draw();
    
    // 画黑色矩形
    shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vBlack);
    blackBatch.Draw();
    
    // 开启颜色混合
    glEnable(GL_BLEND);
    
    // 配置混合方程式
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    
    // 画移动矩形，本身半透明蓝色
    shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vBlue);
    squareBatch.Draw();
    
    // 关闭颜色混合
    glDisable(GL_BLEND);
    
    // 将在后台缓冲区进行渲染，然后在结束时交换到前台
    glutSwapBuffers();
}

// 窗口大小改变时接受新的宽度和高度
void ChangeSize(int w, int h) {
    // 设置视图窗口位置
    glViewport(0, 0, w, h);
}

// 程序入口
int main(int argc, char *argv[]) {
    // 设置当前工作目录，针对Mac OS X
    gltSetWorkingDirectory(argv[0]);
    
    // 初始化GLUT库
    glutInit(&argc, argv);
    
    /*
     初始化渲染模式，其中标志GLUT_DOUBLE、GLUT_RGBA、GLUT_DEPTH、GLUT_STENCILf分别指双缓冲窗口、RGBA颜色模式、深度测试、模板缓冲区
     */
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);
    
    // 初始化窗口大小
    glutInitWindowSize(800, 720);
    
    // 创建窗口
    glutCreateWindow("Move Block with Arror Keys to see blending");
    
    // 注册回调函数
    glutReshapeFunc(ChangeSize);
    glutDisplayFunc(RenderScene);
    glutSpecialFunc(SpecialKeys);
    
    // 确保驱动程序的初始化中没有出现任何问题
    GLenum err = glewInit();
    if (err != GLEW_OK) {
        fprintf(stderr, "glew error:%s\n", glewGetErrorString(err));
        return 1;
    }
    
    // 初始化设置
    SetupRC();
    
    // 进入调用循环
    glutMainLoop();
    
    return 0;
}

运行代码的效果图：