OpenGL 正方形相关操作

一、绘制正方形

1.png 2.png

定义顶点到原心距离，即 正方形边长 = blockSize * 2

//blockSize 边长
GLfloat blockSize = 0.1f;

修改顶点数组

//正方形的4个点坐标
GLfloat vVerts[] = {
        -blockSize,-blockSize,0.0f,
        blockSize,-blockSize,0.0f,
        blockSize,blockSize,0.0f,
        -blockSize,blockSize,0.0f
};

收到渲染消息执行：

3.png

1、清除一个或者一组特定的缓存区
GL_COLOR_BUFFER_BIT :指示当前激活的用来进行颜色写入缓冲区
GL_DEPTH_BUFFER_BIT :指示深度缓存区
GL_STENCIL_BUFFER_BIT:指示模板缓冲区
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT|GL_STENCIL_BUFFER_BIT);

 2、设置一组浮点数来表示红色
 GLfloat vRed[] = {1.0,0.0,0.0,1.0f};

3、 提交着色器
 triangleBatch.Draw();

4、将后台缓冲区进行渲染，然后结束后交换给前台
 glutSwapBuffers();

修改setupRC函数中图元的连接方式

设置清屏颜色（背景颜色）
 glClearColor(0.98f, 0.40f, 0.7f, 1);

修改为GL_TRIANGLE_FAN ，4个顶点
  triangleBatch.Begin(GL_TRIANGLE_FAN, 4);
  triangleBatch.CopyVertexData3f(vVerts);
  triangleBatch.End();

二、特殊键位移动函数

1、坐标更新方式

4.png

void SpecialKeys(int key, int x, int y){
    
    GLfloat stepSize = 0.025f;
    
    GLfloat blockX = vVerts[0];
    GLfloat blockY = vVerts[10];
    
    printf("v[0] = %f\n",blockX);
    printf("v[10] = %f\n",blockY);
    
    
    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;
    }

    //触碰到边界（4个边界）的处理
    
    //当正方形移动超过最左边的时候
    if (blockX < -1.0f) {
        blockX = -1.0f;
    }
    
    //当正方形移动到最右边时
    //1.0 - blockSize * 2 = 总边长 - 正方形的边长 = 最左边点的位置
    if (blockX > (1.0 - blockSize * 2)) {
        blockX = 1.0f - blockSize * 2;
    }
    
    //当正方形移动到最下面时
    //-1.0 - blockSize * 2 = Y（负轴边界） - 正方形边长 = 最下面点的位置
    if (blockY < -1.0f + blockSize * 2 ) {
        
        blockY = -1.0f + blockSize * 2;
    }
    
    //当正方形移动到最上面时
    if (blockY > 1.0f) {
        
        blockY = 1.0f;
        
    }

    printf("blockX = %f\n",blockX);
    printf("blockY = %f\n",blockY);
    
    // Recalculate vertex positions
    vVerts[0] = blockX;
    vVerts[1] = blockY - blockSize*2;
    printf("(%f,%f)\n",vVerts[0],vVerts[1]);
    
    vVerts[3] = blockX + blockSize*2;
    vVerts[4] = blockY - blockSize*2;
    printf("(%f,%f)\n",vVerts[3],vVerts[4]);
    
    vVerts[6] = blockX + blockSize*2;
    vVerts[7] = blockY;
    printf("(%f,%f)\n",vVerts[6],vVerts[7]);
    
    vVerts[9] = blockX;
    vVerts[10] = blockY;
    printf("(%f,%f)\n",vVerts[9],vVerts[10]);
    
    triangleBatch.CopyVertexData3f(vVerts);
    
    glutPostRedisplay();
}

2、矩阵方法

收到消息渲染—>RenderScene函数

5.png

glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT|GL_STENCIL_BUFFER_BIT);
    
    GLfloat vRed[] = {1.0f,0.0f,0.0f,0.0f};
    
    M3DMatrix44f mFinalTransform,mTransfromMatrix,mRotationMartix;
    
    //平移
    m3dTranslationMatrix44(mTransfromMatrix, xPos, yPos, 0.0f);
    
    //每次平移时，旋转5度
    static float yRot = 0.0f;
    yRot += 5.0f;
    m3dRotationMatrix44(mRotationMartix, m3dDegToRad(yRot), 0.0f, 0.0f, 1.0f);
    
    //将旋转和移动的矩阵结果 合并到mFinalTransform （矩阵相乘）
    m3dMatrixMultiply44(mFinalTransform, mTransfromMatrix, mRotationMartix);
    
    //将矩阵结果 提交给固定着色器（平面着色器）中绘制
    shaderManager.UseStockShader(GLT_SHADER_FLAT,mFinalTransform,vRed);
    triangleBatch.Draw();
    
    //执行交换缓存区
    glutSwapBuffers();

矩阵方式的SpecialKeys函数

6.png

void SpecialKeys(int key, int x, int y){
    GLfloat stepSize = 0.025f;
 
    if (key == GLUT_KEY_UP) {
        
        yPos += stepSize;
    }
    
    if (key == GLUT_KEY_DOWN) {
        yPos -= stepSize;
    }
    
    if (key == GLUT_KEY_LEFT) {
        xPos -= stepSize;
    }
    
    if (key == GLUT_KEY_RIGHT) {
        xPos += stepSize;
    }
    
    //碰撞检测
    if (xPos < (-1.0f + blockSize)) {
        
        xPos = -1.0f + blockSize;
    }
    
    if (xPos > (1.0f - blockSize)) {
        xPos = 1.0f - blockSize;
    }
    
    if (yPos < (-1.0f + blockSize)) {
        yPos = -1.0f + blockSize;
    }
    
    if (yPos > (1.0f - blockSize)) {
        yPos = 1.0f - blockSize;
    }
    glutPostRedisplay();
}

参考：https://www.jianshu.com/p/acb2f3a1cc2e