二、OpenGL绘制正方形并用键位移动

一、基础设置

初始化GLUT库，初始化双缓冲窗口

glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGBA|GLUT_DEPTH|GLUT_STENCIL);

设置窗口大小，窗口标题

glutInitWindowSize(500, 500);
glutCreateWindow("Triangle");

注册重塑函数 显示函数 特殊键位函数

glutReshapeFunc(changeSize);
glutDisplayFunc(RenderScene);
glutSpecialFunc(SpecialKeys);

设置渲染函数，开启runloop

setupRC();
glutMainLoop();

二、画正方形

设置顶点坐标

GLfloat blockSize = 0.1f;
GLfloat vVerts[] = {
    -blockSize,-blockSize,0.0f,
    blockSize,-blockSize,0.0f,
    blockSize,blockSize,0.0f,
    -blockSize,blockSize,0.0f
};

初始化着色器，设置画图方式

void setupRC()
{
  glClearColor(0.98f, 0.40f, 0.7f, 1);
  shaderManager.InitializeStockShaders();

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

渲染

void RenderScene(void)
{

  //1.清除一个或者一组特定的缓存区
  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};

  //传递到存储着色器，即GLT_SHADER_IDENTITY着色器
  shaderManager.UseStockShader(GLT_SHADER_IDENTITY,vRed);

  //提交着色器
  triangleBatch.Draw();

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

三、通过键盘操作移动正方形

设置步长，取出一个顶点当做相对顶点使用

GLfloat stepSize = 0.025f;

GLfloat blockX = vVerts[0];
GLfloat blockY = vVerts[10];

根据键盘输入计算顶点位置

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;
}

边界检测

//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
if (blockX > (1.0 - blockSize * 2)) {
    blockX = 1.0f - blockSize * 2;
}

//当正方形移动到最下面时
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;
    
}

计算其他顶点移动后的位置

// 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]);

重新绘制，移动正方形

triangleBatch.CopyVertexData3f(vVerts);
glutPostRedisplay();