Hey guys, I cant seem to get the stencil buffer working properly.
Here is the code.
/*
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* and open the template in the editor.
*/
package chapter3;
import org.lwjgl.LWJGLException;
import org.lwjgl.opengl.Display;
import org.lwjgl.opengl.DisplayMode;
import static org.lwjgl.opengl.GL11.*;
public class Stencil {
// Square position and size variables
private float x1;
private float y1;
private float rsize;
// Step size in x and y directions
// (number of pixels to move each time)
private float xstep;
private float ystep;
// Clipping area variables
private float clipWidth;
private float clipHeight;
public Stencil() {
// Initialize variables
x1 = 0.0f;
y1 = 0.0f;
rsize = 25;
xstep = 1.0f;
ystep = 1.0f;
// Create window
try {
Display.setDisplayMode(new DisplayMode(800, 600));
Display.setTitle("Stencil Animation");
Display.create();
Display.setResizable(true);
Display.setVSyncEnabled(true);
} catch (LWJGLException e) {
e.printStackTrace();
}
}
/*
* Called to run the program
*/
public void run() {
while (!Display.isCloseRequested()) {
setupRC();
changeSize(Display.getWidth(), Display.getHeight());
animate(Display.getWidth(), Display.getHeight());
renderScene();
// Update display
Display.update();
// Display.sync(60);
}
cleanUp();
}
/*
* Called to draw scene
*/
public void renderScene() {
double dRadius = 0.1; // Initial radius of spiral
double dAngle;
// Use 0 for clear stencil, enable stencil test
glClearStencil(0);
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; dAngle += 0.1) {
glVertex2d(dRadius * Math.cos(dAngle), dRadius * Math.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(x1, y1, x1 + rsize, y1 - rsize);
}
/*
* Set up the rendering state
*/
public void setupRC() {
// Set clear color to blue
glClearColor(0.0f, 0.0f, 1.0f, 0.0f);
}
/*
* Set up method to adjust window size
*/
public void changeSize(int w, int h) {
float nRange = 100.0f;
// 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)
if (w <= h) {
glOrtho(-nRange, nRange, -nRange * h / w, nRange * h / w,
-nRange, nRange);
clipWidth = nRange;
clipHeight = nRange * h / w;
} else {
glOrtho(-nRange * w / h, nRange * w / h, -nRange, nRange,
-nRange, nRange);
clipWidth = nRange * w / h;
clipHeight = nRange;
}
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
/*
* Check window size and adjust x and y values
* accordingly, animate square
*/
public void animate(float windowWidth, float windowHeight) {
// Reverse direction when you reach left or right edge
// of the screen
if (x1 > clipWidth - rsize || x1 < -clipWidth) {
xstep = -xstep;
}
// Reverse direction when you reach top or bottom edge
if (y1 > clipHeight || y1 < -clipHeight + rsize) {
ystep = -ystep;
}
animate();
// 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 (x1 > (windowWidth - rsize + xstep)) {
x1 = windowWidth - rsize - 1;
} else if (x1 < -(windowWidth + xstep)) {
x1 = -windowWidth - 1;
}
if (y1 > (windowHeight + ystep)) {
y1 = windowHeight - 1;
} else if (y1 < -(windowHeight - rsize + ystep)) {
y1 = -windowHeight + rsize - 1;
}
}
/*
* Move the square around the screen
*/
public void animate() {
x1 += xstep;
y1 += ystep;
}
/*
* Clean up method used to destroy unused objects
*/
public void cleanUp() {
Display.destroy();
}
public static void main(String[] args) {
new Stencil().run();
}
}
Im learning OpenGL through the OpenGL Superbible book. This is an example of using stencil buffer but it doesnt work for me? What am i missing?
