How to texture glDrawElements - opengl

Question

I have no Idea how I would texture something drawn by using glDrawElements?
From what I gather you need to use glTexCoordPointer? but I'm still really confused.
I'll put the whole program here so you can see what I'm doing
public class DrawWater {
public Expr2 func; // The function that is being drawn.
private String functionInput;
private boolean version_1_5; // Check is OpenGL 1.5 is available; set in init().
public boolean dataIsValid; // Set to true whenever data needs to be recomputed.
public double xMax = 5;
public double yMax = 5;
private int[] textures = new int[3]; // Storage For 3 Textures
// This is checked in the display() method before drawing.
/* Buffers to hold the points and normals for the surface. */
private FloatBuffer vBuf = BufferUtil.newFloatBuffer(201 * 201 * 3);
private FloatBuffer nBuf = BufferUtil.newFloatBuffer(201 * 201 * 3);
/* Buffers to hold the indices for drawing the surface and lines with glDrawElements*/
private IntBuffer surfaceIndexBuffer = BufferUtil.newIntBuffer(200 * 201 * 2);
private IntBuffer xLineIndexBuffer = BufferUtil.newIntBuffer(21 * 201);
private IntBuffer yLineIndexBuffer = BufferUtil.newIntBuffer(21 * 201);
/* VBO ID numbers for holding the data when OpenGL version is 1.5 or higher */
private int vertexVBO, normalVBO; // VBO IDs for surface data.
private int xLineVBO, yLineVBO, surfaceVBO; // VBO IDs for index data.
public DrawWater() {
}
public void setup(GL gl, String equ) {
this.functionInput = equ;
this.func = new Expr2(equ);
}
public void draw(GL gl) {
version_1_5 = gl.isExtensionAvailable("GL_VERSION_1_5");
if (gl.isExtensionAvailable("GL_VERSION_1_3")) {
gl.glEnable(GL.GL_MULTISAMPLE);
}
makeElementBuffers(); // Generate lists of indices for glDrawElements. This data never changes.
if (version_1_5) {
// Generate VBOs for the data, and fill the ones that are for index data with
// data from Java nio buffers. The VBOs for index data won't change again and
// so use GL.GL_STATIC_DRAW.
int[] ids = new int[5];
gl.glGenBuffers(5, ids, 0);
this.vertexVBO = ids[0];
this.normalVBO = ids[1];
this.xLineVBO = ids[2];
this.yLineVBO = ids[3];
this.surfaceVBO = ids[4];
gl.glBindBuffer(GL.GL_ARRAY_BUFFER, vertexVBO);
gl.glVertexPointer(3, GL.GL_FLOAT, 0, 0);
gl.glBindBuffer(GL.GL_ARRAY_BUFFER, normalVBO);
gl.glNormalPointer(GL.GL_FLOAT, 0, 0);
gl.glBindBuffer(GL.GL_ARRAY_BUFFER, 0);
gl.glBindBuffer(GL.GL_ELEMENT_ARRAY_BUFFER, surfaceVBO);
gl.glBufferData(GL.GL_ELEMENT_ARRAY_BUFFER, 4 * 2 * 200 * 201, surfaceIndexBuffer, GL.GL_STATIC_DRAW);
gl.glBindBuffer(GL.GL_ELEMENT_ARRAY_BUFFER, xLineVBO);
gl.glBufferData(GL.GL_ELEMENT_ARRAY_BUFFER, 4 * 21 * 201, xLineIndexBuffer, GL.GL_STATIC_DRAW);
gl.glBindBuffer(GL.GL_ELEMENT_ARRAY_BUFFER, yLineVBO);
gl.glBufferData(GL.GL_ELEMENT_ARRAY_BUFFER, 4 * 21 * 201, yLineIndexBuffer, GL.GL_STATIC_DRAW);
gl.glBindBuffer(GL.GL_ELEMENT_ARRAY_BUFFER, 0);
} else {
gl.glVertexPointer(3, GL.GL_FLOAT, 0, vBuf);
gl.glNormalPointer(GL.GL_FLOAT, 0, nBuf);
}
this.dataIsValid = false; // Force recomputation of data with new graph definition.
if (func != null) {
gl.glMaterialfv(GL.GL_FRONT, GL.GL_AMBIENT_AND_DIFFUSE, new float[]{0.7f, 0.7f, 1}, 0);
gl.glMaterialfv(GL.GL_BACK, GL.GL_AMBIENT_AND_DIFFUSE, new float[]{0.8f, 0.8f, 0.5f}, 0);
if (!dataIsValid) {
this.computeSurfaceData();
if (version_1_5) {
// Set up VBOs for surface points and normals. Since these change
// pretty regularly, use GL.GL_DYNAMIC_DRAW.
gl.glBindBuffer(GL.GL_ARRAY_BUFFER, vertexVBO);
gl.glBufferData(GL.GL_ARRAY_BUFFER, 4 * 3 * 201 * 201, vBuf, GL.GL_DYNAMIC_DRAW);
gl.glBindBuffer(GL.GL_ARRAY_BUFFER, normalVBO);
gl.glBufferData(GL.GL_ARRAY_BUFFER, 4 * 3 * 201 * 201, nBuf, GL.GL_DYNAMIC_DRAW);
gl.glBindBuffer(GL.GL_ARRAY_BUFFER, 0);
}
}
gl.glEnableClientState(GL.GL_VERTEX_ARRAY);
gl.glEnableClientState(GL.GL_NORMAL_ARRAY);
this.drawSurface(gl); // Just draw the surface.
gl.glPolygonOffset(1, 1);
gl.glEnable(GL.GL_POLYGON_OFFSET_FILL);
this.drawSurface(gl);
gl.glDisable(GL.GL_POLYGON_OFFSET_FILL);
gl.glDisable(GL.GL_LIGHTING);
gl.glColor3f(0, 0, 0);
gl.glDisableClientState(GL.GL_NORMAL_ARRAY);
gl.glEnable(GL.GL_LIGHTING);
}
gl.glDisableClientState(GL.GL_VERTEX_ARRAY);
gl.glDisableClientState(GL.GL_NORMAL_ARRAY);
}
private void makeElementBuffers() {
for (int i = 0; i < 201; i += 10) { // indices for drawing lines in x-direction
for (int j = 0; j < 201; j++) {
this.xLineIndexBuffer.put(201 * i + j);
}
}
for (int i = 0; i < 201; i += 10) { // indices for drawing lines in y-direction
for (int j = 0; j < 201; j++) {
this.yLineIndexBuffer.put(201 * j + i);
}
}
for (int i = 0; i < 200; i++) { // indices for drawing surface with GL_TRIANGLE_STRIPs
for (int j = 0; j < 201; j++) {
this.surfaceIndexBuffer.put(201 * (i + 1) + j);
this.surfaceIndexBuffer.put(201 * i + j);
}
}
this.xLineIndexBuffer.rewind();
this.yLineIndexBuffer.rewind();
this.surfaceIndexBuffer.rewind();
}
private void computeSurfaceData() {
double xmin = -xMax;
double xmax = xMax;
double ymin = -yMax;
double ymax = yMax;
double xRes = 200;
double yRes = 200;
float[] surfaceData = new float[301 * 3];
float[] normalData = new float[301 * 3];
double dx = (xmax - xmin) / xRes;
double dy = (ymax - ymin) / yRes;
for (int i = 0; i <= xRes; i++) {
int v = 0;
int n = 0;
double y1 = ymin + dy * i;
for (int j = 0; j <= yRes; j++) {
double x = xmin + dx * j;
func.setVariable('x', x);
func.setVariable('y', y1);
double z1 = func.value();
float[] normal1 = computeUnitNormal(x, y1);
surfaceData[v++] = (float) x;
surfaceData[v++] = (float) y1;
surfaceData[v++] = (float) z1;
normalData[n++] = normal1[0];
normalData[n++] = normal1[1];
normalData[n++] = normal1[2];
}
vBuf.put(surfaceData, 0, 201 * 3);
nBuf.put(normalData, 0, 201 * 3);
}
vBuf.rewind();
nBuf.rewind();
dataIsValid = true;
}
/**
* Draw the surface as a series of triangle strips.
*/
private void drawSurface(GL gl) {
if (version_1_5) {
gl.glBindBuffer(GL.GL_ELEMENT_ARRAY_BUFFER, surfaceVBO);
for (int i = 0; i < 200; i++) {
gl.glTexCoordPointer(3, GL.GL_TRIANGLE_STRIP, 402, nBuf);
gl.glDrawElements(GL.GL_TRIANGLE_STRIP, 402, GL.GL_UNSIGNED_INT, 402 * i * 4);
}
gl.glBindBuffer(GL.GL_ELEMENT_ARRAY_BUFFER, 0);
} else {
for (int i = 0; i < 200; i++) {
surfaceIndexBuffer.position(402 * i);
gl.glDrawElements(GL.GL_TRIANGLE_STRIP, 402, GL.GL_UNSIGNED_INT, surfaceIndexBuffer);
}
}
}
/**
* Compute a unit normal to the graph of z = func(x,y).
* This is only an approximation, using nearby points instead
* of exact derivatives.
*/
private float[] computeUnitNormal(double x, double y) {
double epsilon = 0.00001;
func.setVariable('x', x);
func.setVariable('y', y);
double z = this.func.value();
func.setVariable('x', x + epsilon);
double z1 = func.value();
func.setVariable('x', x);
func.setVariable('y', y + epsilon);
double z2 = this.func.value();
// normal is (epsilon,0,z1-z) X (0,epsilon,z2-z)
double a = -epsilon * (z1 - z);
double b = -epsilon * (z2 - z);
double c = epsilon * epsilon;
double length = Math.sqrt(a * a + b * b + c * c);
if (Double.isNaN(length) || Double.isInfinite(length)) {
return new float[]{0, 0, 1};
} else {
return new float[]{(float) (a / length), (float) (b / length), (float) (c / length)};
}
}
private void loadGLTextures(GLAutoDrawable gldrawable) throws IOException {
TextureReader.Texture texture = null;
texture = TextureReader.readTexture("data/images/04.bmp");
GL gl = gldrawable.getGL();
//Create Nearest Filtered Texture
gl.glGenTextures(1, textures, 0);
gl.glBindTexture(GL.GL_TEXTURE_2D, textures[0]);
gl.glTexParameteri(GL.GL_TEXTURE_2D, GL.GL_TEXTURE_MAG_FILTER, GL.GL_LINEAR);
gl.glTexParameteri(GL.GL_TEXTURE_2D, GL.GL_TEXTURE_MIN_FILTER, GL.GL_LINEAR);
gl.glTexImage2D(GL.GL_TEXTURE_2D,
0,
3,
texture.getWidth(),
texture.getHeight(),
0,
GL.GL_RGB,
GL.GL_UNSIGNED_BYTE,
texture.getPixels());
}
}
Any help or advise would help I'm just confused ?
Ya this is the array buffer
int[] ids = new int[5];
gl.glGenBuffers(5, ids, 0);
this.vertexVBO = ids[0];
this.normalVBO = ids[1];
this.xLineVBO = ids[2];
this.yLineVBO = ids[3];
this.surfaceVBO = ids[4];
gl.glBindBuffer(GL.GL_ARRAY_BUFFER, vertexVBO);
gl.glVertexPointer(3, GL.GL_FLOAT, 0, 0);
gl.glBindBuffer(GL.GL_ARRAY_BUFFER, normalVBO);
gl.glNormalPointer(GL.GL_FLOAT, 0, 0);
gl.glBindBuffer(GL.GL_ARRAY_BUFFER, 0);
gl.glBindBuffer(GL.GL_ELEMENT_ARRAY_BUFFER, surfaceVBO);
gl.glBufferData(GL.GL_ELEMENT_ARRAY_BUFFER, 4 * 2 * 200 * 201, surfaceIndexBuffer, GL.GL_STATIC_DRAW);
gl.glBindBuffer(GL.GL_ELEMENT_ARRAY_BUFFER, xLineVBO);
gl.glBufferData(GL.GL_ELEMENT_ARRAY_BUFFER, 4 * 21 * 201, xLineIndexBuffer, GL.GL_STATIC_DRAW);
gl.glBindBuffer(GL.GL_ELEMENT_ARRAY_BUFFER, yLineVBO);
gl.glBufferData(GL.GL_ELEMENT_ARRAY_BUFFER, 4 * 21 * 201, yLineIndexBuffer, GL.GL_STATIC_DRAW);
I can add the whole program if you'd like to see?

Answer 1

As you have created (I hope) a GL_ARRAY_BUFFER with your vertices and set it with glVertexPointer, you should create a GL_ARRAY_BUFFER with your texture coordinates and set it using glTexCoordPointer. Could you copy paste your glVertexPointer call?