opengl超级宝典代码3
第三个例子是第二章的最后一个例子－－bounce
代码如下：
// Initial square position and size
GLfloat x = 0.0f;
GLfloat y = 0.0f;
GLfloat rsize = 25;
// Step size in x and y directions
// (number of pixels to move each time)
GLfloat xstep = 1.0f;
GLfloat ystep = 1.0f;
// Keep track of windows changing width and height
GLfloat windowWidth;
GLfloat windowHeight;
///////////////////////////////////////////////////////////
// Called to draw scene
void RenderScene(void)
{
// Clear the window with current clearing color
glClear(GL_COLOR_BUFFER_BIT);
// Set current drawing color to red
// R G B
glColor3f(1.0f, 0.0f, 0.0f);
// Draw a filled rectangle with current color
glRectf(x, y, x + rsize, y - rsize);
// Flush drawing commands and swap
glutSwapBuffers();
}
///////////////////////////////////////////////////////////
// Called by GLUT library when idle (window not being
// resized or moved)
void TimerFunction(int value)
{
// Reverse direction when you reach left or right edge
if(x > windowWidth-rsize || x < -windowWidth)
xstep = -xstep;
// Reverse direction when you reach top or bottom edge
if(y > windowHeight || y < -windowHeight + rsize)
ystep = -ystep;
// Actually move the square
x += xstep;
y += ystep;
// Check bounds. This is in case the window is made
// smaller while the rectangle is bouncing and the
// rectangle suddenly finds itself outside the new
// clipping volume
if(x > (windowWidth-rsize + xstep))
x = windowWidth-rsize-1;
else if(x < -(windowWidth + xstep))
x = -windowWidth -1;
if(y > (windowHeight + ystep))
y = windowHeight-1;
else if(y < -(windowHeight - rsize + ystep))
y = -windowHeight + rsize - 1;
// Redraw the scene with new coordinates
glutPostRedisplay();
glutTimerFunc(33,TimerFunction, 1);
}
///////////////////////////////////////////////////////////
// Setup the rendering state
void SetupRC(void)
{
// Set clear color to blue
glClearColor(0.0f, 0.0f, 1.0f, 1.0f);
}
///////////////////////////////////////////////////////////
// Called by GLUT library when the window has chanaged size
void ChangeSize(int w, int h)
{
GLfloat aspectRatio;
// Prevent a divide by zero
if(h == 0)
h = 1;
// Set Viewport to window dimensions
glViewport(0, 0, w, h);
// Reset coordinate system
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
// Establish clipping volume (left, right, bottom, top, near, far)
aspectRatio = (GLfloat)w / (GLfloat)h;
if (w <= h)
{
windowWidth = 100;
windowHeight = 100 / aspectRatio;
glOrtho (-100.0, 100.0, -windowHeight, windowHeight, 1.0, -1.0);
}
else
{
windowWidth = 100 * aspectRatio;
windowHeight = 100;
glOrtho (-windowWidth, windowWidth, -100.0, 100.0, 1.0, -1.0);
}
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
///////////////////////////////////////////////////////////
// Main program entry point
int main(int argc, char* argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);
glutInitWindowSize(800,600);
glutCreateWindow("Bounce");
glutDisplayFunc(RenderScene);
glutReshapeFunc(ChangeSize);
glutTimerFunc(33, TimerFunction, 1);
SetupRC();
glutMainLoop();
return 0;
}
我们不再分析在前两个例子中出现的函数。
第一个地方是如何使用timer，使用的函数glutTimerFunc(33,TimerFunction, 1);，这里第一个参数是毫秒，第二个是timer触发的函数，第三个是传入的参数，注意这个timer每次都只触发一次。
第二个地方是glutPostRedisplay();，它所作的就是强制刷新界面。
第三个地方就是在对显示模式初始化的时候的参数GLUT_DOUBLE，它表示使用双缓存模式，和GLUT_SINGLE不同的是，双缓存方式调用glutSwapBuffers来把还没有刷新的命令效果刷新到，后者使用
glutSwapBuffers
做这个事情。