کد:
// Stencil.c
// OpenGL SuperBible, 3rd Edition
// Richard S. Wright Jr.
// rwright@starstonesoftware.com
#include "../../Common/OpenGLSB.h" // System and OpenGL Stuff
// 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)
{
GLdouble dRadius = 0.1; // Initial radius of spiral
GLdouble dAngle; // Looping variable
// Clear blue window
glClearColor(0.0f, 0.0f, 1.0f, 0.0f);
// Use 0 for clear stencil, enable stencil test
glClearStencil(0.0f);
glEnable(GL_STENCIL_TEST);
// Clear color and stencil buffer
glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
// All drawing commands fail the stencil test, and are not
// drawn, but increment the value in the stencil buffer.
glStencilFunc(GL_NEVER, 0x0, 0x0);
glStencilOp(GL_INCR, GL_INCR, GL_INCR);
// Spiral pattern will create stencil pattern
// Draw the spiral pattern with white lines. We
// make the lines white to demonstrate that the
// stencil function prevents them from being drawn
glColor3f(1.0f, 1.0f, 1.0f);
glBegin(GL_LINE_STRIP);
for(dAngle = 0; dAngle < 400.0; dAngle += 0.1)
{
glVertex2d(dRadius * cos(dAngle), dRadius * sin(dAngle));
dRadius *= 1.002;
}
glEnd();
// Now, allow drawing, except where the stencil pattern is 0x1
// and do not make any further changes to the stencil buffer
glStencilFunc(GL_NOTEQUAL, 0x1, 0x1);
glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
// Now draw red bouncing square
// (x and y) are modified by a timer function
glColor3f(1.0f, 0.0f, 0.0f);
glRectf(x, y, x + rsize, y - rsize);
// All done, do the buffer 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;
// 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)
x = windowWidth-rsize-1;
if(y > windowHeight)
y = windowHeight-1;
// Actually move the square
x += xstep;
y += ystep;
// Redraw the scene with new coordinates
glutPostRedisplay();
glutTimerFunc(33,TimerFunction, 1);
}
///////////////////////////////////////////////////////////
// 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();
}
///////////////////////////////////////////////////////////
// Program entry point
int main(int argc, char* argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_STENCIL);
glutInitWindowSize(800,600);
glutCreateWindow("OpenGL Stencil Test");
glutReshapeFunc(ChangeSize);
glutDisplayFunc(RenderScene);
glutTimerFunc(33, TimerFunction, 1);
glutMainLoop();
return 0;
}
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