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This example shows how to create extremely realistic reflections using the stencil buffer, clipping, and multi-texturing.
This is the Java port of the one of the NeHe OpenGL tutorials.
You can get complete IntelliJ IDEA project structure (all source, resources, build script, …) by downloading the source distribution from here.
The original post of the programmer who ported the examples can be found here.
package demos.nehe.lesson26;
import demos.common.GLDisplay;
/**
* @author Pepijn Van Eeckhoudt
*/
public class Lesson26 {
public static void main(String[] args) {
GLDisplay neheGLDisplay = GLDisplay.createGLDisplay("Lesson 26: Reflections");
Renderer renderer = new Renderer();
InputHandler inputHandler = new InputHandler(renderer, neheGLDisplay);
neheGLDisplay.addGLEventListener(renderer);
neheGLDisplay.addKeyListener(inputHandler);
neheGLDisplay.start();
}
}
package demos.nehe.lesson26;
import demos.common.GLDisplay;
import javax.swing.*;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
class InputHandler extends KeyAdapter {
private Renderer renderer;
public InputHandler(Renderer renderer, GLDisplay glDisplay) {
this.renderer = renderer;
glDisplay.registerKeyStrokeForHelp(
KeyStroke.getKeyStroke(KeyEvent.VK_PAGE_UP, 0), "Move ball up");
glDisplay.registerKeyStrokeForHelp(
KeyStroke.getKeyStroke(KeyEvent.VK_PAGE_DOWN, 0), "Move ball down");
glDisplay.registerKeyStrokeForHelp(
KeyStroke.getKeyStroke(KeyEvent.VK_A, 0), "Zoom in");
glDisplay.registerKeyStrokeForHelp(
KeyStroke.getKeyStroke(KeyEvent.VK_Z, 0), "Zoom out");
glDisplay.registerKeyStrokeForHelp(
KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0),
"Decrease X-axis rotation speed");
glDisplay.registerKeyStrokeForHelp(
KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0),
"Increase X-axis rotation speed");
glDisplay.registerKeyStrokeForHelp(
KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0),
"Decrease Y-axis rotation speed");
glDisplay.registerKeyStrokeForHelp(
KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0),
"Increase Y-axis rotation speed");
}
public void keyPressed(KeyEvent e) {
processKeyEvent(e, true);
}
public void keyReleased(KeyEvent e) {
processKeyEvent(e, false);
}
private void processKeyEvent(KeyEvent e, boolean pressed) {
switch (e.getKeyCode()) {
case KeyEvent.VK_A:
renderer.zoomIn(pressed);
break;
case KeyEvent.VK_Z:
renderer.zoomOut(pressed);
break;
case KeyEvent.VK_PAGE_UP:
renderer.increaseHeight(pressed);
break;
case KeyEvent.VK_PAGE_DOWN:
renderer.decreaseHeight(pressed);
break;
case KeyEvent.VK_UP:
renderer.decreaseXspeed(pressed);
break;
case KeyEvent.VK_DOWN:
renderer.increaseXspeed(pressed);
break;
case KeyEvent.VK_RIGHT:
renderer.increaseYspeed(pressed);
break;
case KeyEvent.VK_LEFT:
renderer.decreaseYspeed(pressed);
break;
}
}
}
package demos.nehe.lesson26;
import demos.common.TextureReader;
import javax.media.opengl.*;
import javax.media.opengl.glu.GLUquadric;
import javax.media.opengl.glu.GLU;
import java.io.IOException;
class Renderer implements GLEventListener {
private float xrot = 0f; // X Rotation
private float yrot = 0f; // Y Rotation
private float xspeed = 0f; // X Rotation Speed
private boolean increaseXspeed;
private boolean decreaseXspeed;
private float yspeed = 0f; // Y Rotation Speed
private boolean increaseYspeed;
private boolean decreaseYspeed;
private float zoom = -7.0f; // Depth Into The Screen
private boolean zoomIn;
private boolean zoomOut;
private float height = 2.0f; // Height Of Ball From Floor
private boolean increaseHeight;
private boolean decreaseHeight;
private int textures[] = new int[3]; // Storage For 6 Textures (Modified)
private float lightAmbient[] = {0.2f, 0.2f, 0.2f}; // Ambient Light is 20% white
private float lightDiffuse[] = {1.0f, 1.0f, 1.0f}; // Diffuse Light is white
// Position is somewhat in front of screen
private float lightPosition[] = {0.0f, 0.0f, 2.0f};
private GLUquadric q; // Storage For Our Quadratic Objects
private GLU glu = new GLU();
public Renderer() {
}
public float getZoom() {
return zoom;
}
public void zoomIn(boolean zoom) {
zoomIn = zoom;
}
public void zoomOut(boolean zoom) {
zoomOut = zoom;
}
public void increaseHeight(boolean increase) {
increaseHeight = increase;
}
public void decreaseHeight(boolean decrease) {
decreaseHeight = decrease;
}
public void increaseXspeed(boolean increase) {
increaseXspeed = increase;
}
public void decreaseXspeed(boolean decrease) {
decreaseXspeed = decrease;
}
public void increaseYspeed(boolean increase) {
increaseYspeed = increase;
}
public void decreaseYspeed(boolean decrease) {
decreaseYspeed = decrease;
}
public void loadGLTextures(GL gl) throws IOException {
String[] textureNames = new String[]{
"demos/data/images/envwall.jpg",
"demos/data/images/ball.jpg",
"demos/data/images/envroll.jpg"
};
gl.glGenTextures(3, textures, 0); // Create The Texture
for (int loop = 0; loop < 3; loop++) // Loop Through 5 Textures
{
String textureName = textureNames[loop];
TextureReader.Texture texture = TextureReader.readTexture(textureName);
gl.glBindTexture(GL.GL_TEXTURE_2D, textures[loop]);
gl.glTexImage2D(GL.GL_TEXTURE_2D, 0, GL.GL_RGB8, texture.getWidth(),
texture.getHeight(), 0, GL.GL_RGB, GL.GL_UNSIGNED_BYTE,
texture.getPixels());
gl.glTexParameteri(GL.GL_TEXTURE_2D, GL.GL_TEXTURE_MIN_FILTER,
GL.GL_LINEAR);
gl.glTexParameteri(GL.GL_TEXTURE_2D, GL.GL_TEXTURE_MAG_FILTER,
GL.GL_LINEAR);
}
}
public void init(GLAutoDrawable glDrawable) {
GL gl = glDrawable.getGL();
try {
loadGLTextures(gl); // If Loading The Textures Failed
} catch (IOException e) {
throw new RuntimeException(e);
}
gl.glShadeModel(GL.GL_SMOOTH); // Enable Smooth Shading
gl.glClearColor(0.2f, 0.5f, 1.0f, 1.0f); // Background
gl.glClearDepth(1.0f); // Depth Buffer Setup
gl.glClearStencil(0); // Clear The Stencil Buffer To 0
gl.glEnable(GL.GL_DEPTH_TEST); // Enables Depth Testing
gl.glDepthFunc(GL.GL_LEQUAL); // The Type Of Depth Testing To Do
// Really Nice Perspective Calculations
gl.glHint(GL.GL_PERSPECTIVE_CORRECTION_HINT, GL.GL_NICEST);
gl.glEnable(GL.GL_TEXTURE_2D); // Enable 2D Texture Mapping
// Set The Ambient Lighting For Light0
gl.glLightfv(GL.GL_LIGHT0, GL.GL_AMBIENT, lightAmbient, 0);
// Set The Diffuse Lighting For Light0
gl.glLightfv(GL.GL_LIGHT0, GL.GL_DIFFUSE, lightDiffuse, 0);
// Set The Position For Light0
gl.glLightfv(GL.GL_LIGHT0, GL.GL_POSITION, lightPosition, 0);
gl.glEnable(GL.GL_LIGHT0); // Enable Light 0
gl.glEnable(GL.GL_LIGHTING); // Enable Lighting
q = glu.gluNewQuadric(); // Create A New Quadratic
glu.gluQuadricNormals(q, GL.GL_SMOOTH); // Generate Smooth Normals For The Quad
glu.gluQuadricTexture(q, true); // Enable Texture Coords For The Quad
// Set Up Sphere Mapping
gl.glTexGeni(GL.GL_S, GL.GL_TEXTURE_GEN_MODE, GL.GL_SPHERE_MAP);
// Set Up Sphere Mapping
gl.glTexGeni(GL.GL_T, GL.GL_TEXTURE_GEN_MODE, GL.GL_SPHERE_MAP);
}
private void DrawObject(GL gl, GLU glu) // Draw Our Ball
{
gl.glColor3f(1.0f, 1.0f, 1.0f); // Set Color To White
gl.glBindTexture(GL.GL_TEXTURE_2D, textures[1]);// Select Texture 2 (1)
glu.gluSphere(q, 0.35f, 32, 16); // Draw First Sphere
gl.glBindTexture(GL.GL_TEXTURE_2D, textures[2]);// Select Texture 3 (2)
gl.glColor4f(1.0f, 1.0f, 1.0f, 0.4f); // Set Color To White With 40% Alpha
gl.glEnable(GL.GL_BLEND); // Enable Blending
// Set Blending Mode To Mix Based On SRC Alpha
gl.glBlendFunc(GL.GL_SRC_ALPHA, GL.GL_ONE);
gl.glEnable(GL.GL_TEXTURE_GEN_S); // Enable Sphere Mapping
gl.glEnable(GL.GL_TEXTURE_GEN_T); // Enable Sphere Mapping
glu.gluSphere(q, 0.35f, 32, 16); // Draw Another Sphere Using New Texture
// Textures Will Mix Creating A MultiTexture Effect (Reflection)
gl.glDisable(GL.GL_TEXTURE_GEN_S); // Disable Sphere Mapping
gl.glDisable(GL.GL_TEXTURE_GEN_T); // Disable Sphere Mapping
gl.glDisable(GL.GL_BLEND); // Disable Blending
}
private void DrawFloor(GL gl) // Draws The Floor
{
gl.glBindTexture(GL.GL_TEXTURE_2D, textures[0]); // Select Texture 1 (0)
gl.glBegin(GL.GL_QUADS); // Begin Drawing A Quad
gl.glNormal3f(0.0f, 1.0f, 0.0f); // Normal Pointing Up
gl.glTexCoord2f(0.0f, 1.0f); // Bottom Left Of Texture
gl.glVertex3f(-2.0f, 0.0f, 2.0f); // Bottom Left Corner Of Floor
gl.glTexCoord2f(0.0f, 0.0f); // Top Left Of Texture
gl.glVertex3f(-2.0f, 0.0f, -2.0f); // Top Left Corner Of Floor
gl.glTexCoord2f(1.0f, 0.0f); // Top Right Of Texture
gl.glVertex3f(2.0f, 0.0f, -2.0f); // Top Right Corner Of Floor
gl.glTexCoord2f(1.0f, 1.0f); // Bottom Right Of Texture
gl.glVertex3f(2.0f, 0.0f, 2.0f); // Bottom Right Corner Of Floor
gl.glEnd(); // Done Drawing The Quad
}
private void update() {
if (zoomIn)
zoom += 0.05f;
if (zoomOut)
zoom -= 0.05f;
if (increaseHeight)
height += 0.03f;
if (decreaseHeight)
height -= 0.03f;
if (increaseXspeed)
xspeed += 0.08f;
if (decreaseXspeed)
xspeed -= 0.08f;
if (increaseYspeed)
yspeed += 0.08f;
if (decreaseYspeed)
yspeed -= 0.08f;
}
public void display(GLAutoDrawable glDrawable) {
update();
GL gl = glDrawable.getGL();
// Clear Screen, Depth Buffer & Stencil Buffer
gl.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT |
GL.GL_STENCIL_BUFFER_BIT);
// Clip Plane Equations
// Plane Equation To Use For The Reflected Objects
double eqr[] = {0.0f, -1.0f, 0.0f, 0.0f};
gl.glLoadIdentity(); // Reset The Modelview Matrix
// Zoom And Raise Camera Above The Floor (Up 0.6 Units)
gl.glTranslatef(0.0f, -0.6f, zoom);
gl.glColorMask(false, false, false, false); // Set Color Mask
// Enable Stencil Buffer For "marking" The Floor
gl.glEnable(GL.GL_STENCIL_TEST);
// Always Passes, 1 Bit Plane, 1 As Mask
gl.glStencilFunc(GL.GL_ALWAYS, 1, 1);
// We Set The Stencil Buffer To 1 Where We Draw Any Polygon
gl.glStencilOp(GL.GL_KEEP, GL.GL_KEEP, GL.GL_REPLACE);
// Keep If Test Fails, Keep If Test Passes But Buffer Test Fails
// Replace If Test Passes
gl.glDisable(GL.GL_DEPTH_TEST); // Disable Depth Testing
DrawFloor(gl); // Draw The Floor (Draws To The Stencil Buffer)
// We Only Want To Mark It In The Stencil Buffer
gl.glEnable(GL.GL_DEPTH_TEST); // Enable Depth Testing
gl.glColorMask(true, true, true, true); // Set Color Mask to TRUE, TRUE, TRUE, TRUE
gl.glStencilFunc(GL.GL_EQUAL, 1, 1); // We Draw Only Where The Stencil Is 1
// (I.E. Where The Floor Was Drawn)
// Don't Change The Stencil Buffer
gl.glStencilOp(GL.GL_KEEP, GL.GL_KEEP, GL.GL_KEEP);
gl.glEnable(GL.GL_CLIP_PLANE0); // Enable Clip Plane For Removing Artifacts
// (When The Object Crosses The Floor)
gl.glClipPlane(GL.GL_CLIP_PLANE0, eqr, 0); // Equation For Reflected Objects
gl.glPushMatrix(); // Push The Matrix Onto The Stack
gl.glScalef(1.0f, -1.0f, 1.0f); // Mirror Y Axis
gl.glLightfv(GL.GL_LIGHT0, GL.GL_POSITION, lightPosition, 0); // Set Up Light0
gl.glTranslatef(0.0f, height, 0.0f); // Position The Object
gl.glRotatef(xrot, 1.0f, 0.0f, 0.0f); // Rotate Local Coordinate System On X Axis
gl.glRotatef(yrot, 0.0f, 1.0f, 0.0f); // Rotate Local Coordinate System On Y Axis
DrawObject(gl, glu); // Draw The Sphere (Reflection)
gl.glPopMatrix(); // Pop The Matrix Off The Stack
gl.glDisable(GL.GL_CLIP_PLANE0); // Disable Clip Plane For Drawing The Floor
gl.glDisable(GL.GL_STENCIL_TEST); // We Don't Need The Stencil Buffer Any More (Disable)
gl.glLightfv(GL.GL_LIGHT0, GL.GL_POSITION, lightPosition, 0); // Set Up Light0 Position
gl.glEnable(GL.GL_BLEND); // Enable Blending (Otherwise The Reflected Object Wont Show)
gl.glDisable(GL.GL_LIGHTING); // Since We Use Blending, We Disable Lighting
gl.glColor4f(1.0f, 1.0f, 1.0f, 0.8f); // Set Color To White With 80% Alpha
// Blending Based On Source Alpha And 1 Minus Dest Alpha
gl.glBlendFunc(GL.GL_SRC_ALPHA, GL.GL_ONE_MINUS_SRC_ALPHA);
DrawFloor(gl); // Draw The Floor To The Screen
gl.glEnable(GL.GL_LIGHTING); // Enable Lighting
gl.glDisable(GL.GL_BLEND); // Disable Blending
gl.glTranslatef(0.0f, height, 0.0f); // Position The Ball At Proper Height
gl.glRotatef(xrot, 1.0f, 0.0f, 0.0f); // Rotate On The X Axis
gl.glRotatef(yrot, 0.0f, 1.0f, 0.0f); // Rotate On The Y Axis
DrawObject(gl, glu); // Draw The Ball
xrot += xspeed; // Update X Rotation Angle By xrotspeed
yrot += yspeed; // Update Y Rotation Angle By yrotspeed
}
public void reshape(GLAutoDrawable glDrawable, int x, int y, int w, int h) {
if (h == 0) h = 1;
GL gl = glDrawable.getGL();
// Reset The Current Viewport And Perspective Transformation
gl.glViewport(0, 0, w, h);
gl.glMatrixMode(GL.GL_PROJECTION); // Select The Projection Matrix
gl.glLoadIdentity(); // Reset The Projection Matrix
// Calculate The Aspect Ratio Of The Window
glu.gluPerspective(45.0f, (float) w / (float) h, 0.1f, 100.0f);
gl.glMatrixMode(GL.GL_MODELVIEW); // Select The Modelview Matrix
gl.glLoadIdentity(); // Reset The ModalView Matrix
}
public void displayChanged(GLAutoDrawable glDrawable, boolean b, boolean b1) {
}
}
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