Draw mesh on image in openGL ES

OpenGL OpenGL: Basic Coding
1

Hello,
I am newbie. I tried to create a mesh in openGL ES. But somewhere I am making some mistake. Can anyone show me the correct way to do this??? I just want to create a 2D mesh.
Also I want to map mesh with an image. Since I am developing under Iphone environment, I am not able to use GLU utility. Please help asap…
Thanks in advance. My question may be childish but I need to sort this

This is my setup View:

-(void)setupView:(GLView*)view
{
const GLfloat zNear = 0.01, zFar = 1000.0, fieldOfView = 45.0;
GLfloat size;
glEnable(GL_DEPTH_TEST);
glMatrixMode(GL_PROJECTION);
size = zNear * tanf(DEGREES_TO_RADIANS(fieldOfView) / 2.0);
CGRect rect = view.bounds;
glFrustumf(-size, size, -size / (rect.size.width / rect.size.height), size /
(rect.size.width / rect.size.height), zNear, zFar);
glViewport(0, 0, rect.size.width, rect.size.height);
glMatrixMode(GL_MODELVIEW);

// Turn necessary features on
glEnable(GL_TEXTURE_2D);
glEnable(GL_BLEND);
glBlendFunc(GL_ONE, GL_SRC_COLOR);


glGenTextures(1, &texture[0]);
glBindTexture(GL_TEXTURE_2D, texture[0]);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR); 
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);

NSString *path = [[NSBundle mainBundle] pathForResource:@“texture” ofType:@“png”];
NSData *texData = [[NSData alloc] initWithContentsOfFile:path];
UIImage *image = [[UIImage alloc] initWithData:texData];

if (image == nil)
    NSLog(@"Do real error checking here");

GLuint width = CGImageGetWidth(image.CGImage);
GLuint height = CGImageGetHeight(image.CGImage);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
void *imageData = malloc( height * width * 4 );
CGContextRef context = CGBitmapContextCreate( imageData, width, height, 8, 4 * width, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big );

// Flip the Y-axis
CGContextTranslateCTM (context, 0, height);
CGContextScaleCTM (context, 1.0, -1.0);

CGColorSpaceRelease( colorSpace );
CGContextClearRect( context, CGRectMake( 0, 0, width, height ) );
CGContextDrawImage( context, CGRectMake( 0, 0, width, height ), image.CGImage );

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageData);

CGContextRelease(context);

free(imageData);
[image release];
[texData release];


// Turn the first light on
glEnable(GL_LIGHT0);

// Define the ambient component of the first light
static const Color3D light0Ambient[] = {{0.4, 0.4, 0.4, 1.0}};
glLightfv(GL_LIGHT0, GL_AMBIENT, (const GLfloat *)light0Ambient);

// Define the diffuse component of the first light
static const Color3D light0Diffuse[] = {{0.8, 0.8, 0.8, 1.0}};
glLightfv(GL_LIGHT0, GL_DIFFUSE, (const GLfloat *)light0Diffuse);

// Define the position of the first light
// const GLfloat light0Position[] = {10.0, 10.0, 10.0}; 
static const Vertex3D light0Position[] = {{10.0, 10.0, 10.0}};
glLightfv(GL_LIGHT0, GL_POSITION, (const GLfloat *)light0Position); 
[self populateMesh];

}

populateMesh function goes as follows:

-(void)populateMesh{
verticalDivisions = kVerticalDivisions;
horizontalDivisions = kHorisontalDivisions;

unsigned int verticesArrsize = (kVerticalDivisions * ((2 + kHorisontalDivisions * 2) * 3));
unsigned int textureCoordsArraySize = kVerticalDivisions * ((2 + kHorisontalDivisions * 2) * 2);
verticesArr = (GLfloat *)malloc(verticesArrsize * sizeof(GLfloat));
textureCoordsArr = (GLfloat*)malloc(textureCoordsArraySize * sizeof(GLfloat));
if (verticesArr == NULL) {
	NSLog(@"verticesArr = NULL!");
}

float height = kWindowHeight/verticalDivisions;
float width = kWindowWidth/horizontalDivisions;
int i,j;
count = 0;
for (j=0; j<verticalDivisions; j++) {
	for (i=0; i<=horizontalDivisions; i++, count+=6) { //2 vertices each time...
		float currX = i * width;
		float currY = j * height;
		verticesArr[count] = currX;
		verticesArr[count+1] = currY + height;
		verticesArr[count+2] = 0.0f;
		
		verticesArr[count+3] = currX;
		verticesArr[count+4] = currY;
		verticesArr[count+5] = 0.0f;
	} 
}


float xIncrease = 1.0f/horizontalDivisions;
float yIncrease = 1.0f/verticalDivisions;

int x,y;
count = 0;

for (y=0; y<verticalDivisions; y++) {
	for (x=0; x<horizontalDivisions+1; x++, count+=4) {
		float currX = x *xIncrease;
		
		float currY = y * yIncrease;
		textureCoordsArr[count] = (float)currX;
		textureCoordsArr[count+1] = (float)currY + yIncrease;
		
		textureCoordsArr[count+2] = (float)currX;
		textureCoordsArr[count+3] = (float)currY;
	}
}

}

and finally drawView as follows:

  • (void)drawView:(GLView*)view
    {
    static GLfloat rot = 0.0;

    glColor4f(0.0, 0.0, 0.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);

    glLoadIdentity();
    glTranslatef(0.0, 0.0, -1.0);
    glRotatef(rot, 1.0, 1.0, 1.0);

    glBindTexture(GL_TEXTURE_2D, texture[0]);
    glVertexPointer(3, GL_FLOAT, 0, verticesArr);
    glTexCoordPointer(3, GL_FLOAT, 0, textureCoordsArr);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
    glPushMatrix();{
    int i;
    for (i=0; i<verticalDivisions; i++) {
    glDrawArrays(GL_TRIANGLE_STRIP, i*(horizontalDivisions2+2), horizontalDivisions2+2);
    }
    }glPopMatrix();
    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_TEXTURE_COORD_ARRAY);

}

I cant upload resulting image…

2

There are several ways to draw a mesh, not just one. If you could post your code it would help.

3

My question may be childish but I need to sort this

Yes you are right, it is childish. Why? Because you have not even thought about those who are reading this and trying to help you. You give no meaninful information about why it’s not working. You have not posted a single line of code which where you have the problem. You expect everyone else to do the work for you.
For example:

I tried to create a mesh in openGL ES

How? What utility is creating the mesh? Did you code it by hand? Where’s the code in that case?
If you posted code, then we could see if you have included texture coordinates. You can’t texture map without them and all models/meshes usually include verticies, normals and texture coordinates.

but I need to sort this

Sounds like you need to start learning how to develop on the iPhone rather than post seemingly random questions on an OpenGL forum. You need to do more research on the basic setup and environment before getting into specifics.

4

I HAVE POSTED THE CODE. PLEASE HAVE A LOOK…