一、绘制流程

image.png

二、定义正方形顶点数据

blockSize为变长的一半

//blockSize 边长
GLfloat blockSize = 0.1f;

//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
};

image.png

三、键位控制
当正方形上下左右移动的时候，需要更新正方形的位置

实现方式有两种：
1、坐标更新，手动计算每个顶点的位置

    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]);

2、矩阵计算，提供一个顶点x、y轴位置，通过矩阵批量计算，适用于多顶点的图形

image.png

三、代码实现
链接: https://pan.baidu.com/s/1sqglgDskdgWa4tVQbF232g 提取码: 7dfy