A Little Help

I'm having a problem with OpenGL ES, and it's keeping me from finishing my particle engine post. I was hoping someone here could see what I'm doing. Here's the code that I have to draw a texture mapped particle. This version uses GL_TRIANGLES and glDrawArrays(), but I've had similar problems using GL_TRIANGLE_STRIP and glDrawElements()..

    case ParticleEmitter3DDrawTextureMap:
    {
        static const GLfloat squareStrip[18] = {
            +0.01f, +0.01f, +0.0f,
            -0.01f, +0.01f, +0.0f,
            -0.01f, -0.01f, +0.0f,
        
            +0.01f, +0.01f, +0.0f,
            -0.01f, -0.01f, +0.0f,
            +0.01f, -0.01f, +0.0f,
        };
        static const GLfloat tex[12] = {
    
            1.0, 1.0,
            0.0, 1.0,
            0.0, 0.0,
        
            1.0, 1.0,
            0.0, 0.0,
            1.0, 0.0,   
        };
    
        //static const GLfloat squareNormals[6] = {0.0, 0.0, 0.0, 0.0, 0.0, 0.0};
    
        glScalef(oneParticle->particleSize, oneParticle->particleSize, oneParticle->particleSize);
    
        [texture bind];
        glEnable(GL_TEXTURE);
        glEnableClientState(GL_TEXTURE_COORD_ARRAY);
        //glEnableClientState(GL_NORMAL_ARRAY);
        glVertexPointer(3, GL_FLOAT, 0, squareStrip);
        //glNormalPointer(GL_FLOAT, 0, squareNormals);
        glTexCoordPointer(3, GL_FLOAT, 0, tex);
        glDrawArrays(GL_TRIANGLES, 0, 6);
        glDisable(GL_TEXTURE);
        //glDisableClientState(GL_NORMAL_ARRAY);
        glDisableClientState(GL_TEXTURE_COORD_ARRAY);
        break;
    }

As a test, I was mapping this image onto the sprites:

But, what I get is this:

My guess, this is either a texture coordinate issue or a blending function issue. I've tried many, many permutations, both with triangle strips and triangles, and using glDrawArrays() and glDrawElements(), and I've tried every permutation of texture coordinates I can think of, yet I've never been able to get both triangles mapped right.

Here's a slightly different version that gives the same result:

            case ParticleEmitter3DDrawTextureMap:
            {
                static const GLfloat squareVertices[12] = {
                    +0.01f, +0.01f, +0.0f,
                    -0.01f, +0.01f, +0.0f,
                    -0.01f, -0.01f, +0.0f,
                    +0.01f, -0.01f, +0.0f,
                };
                static const GLfloat tex[8] = {
                    1.0, 0.0,
                    0.0, 1.0,
                    0.0, 0.0,
                    1.0, 0.0,
                };
                static const GLushort triangle1[3] = {0,2,1};
                static const GLushort triangle2[3] = {2,3,0};
                
                //static const GLfloat squareNormals[6] = {0.0, 0.0, 0.0, 0.0, 0.0, 0.0};
                
                glScalef(oneParticle->particleSize, oneParticle->particleSize, oneParticle->particleSize);
                
                [texture bind];
                glEnable(GL_TEXTURE);
                glEnableClientState(GL_TEXTURE_COORD_ARRAY);
                //glEnableClientState(GL_NORMAL_ARRAY);
                glVertexPointer(3, GL_FLOAT, 0, squareVertices);
                //glNormalPointer(GL_FLOAT, 0, squareNormals);
                glTexCoordPointer(3, GL_FLOAT, 0, tex);
                //glDrawArrays(GL_TRIANGLES, 0, 6);

                glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_SHORT, &triangle1);
                glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_SHORT, &triangle2);
                glDisable(GL_TEXTURE);
                glDisableClientState(GL_NORMAL_ARRAY);
                glDisableClientState(GL_TEXTURE_COORD_ARRAY);
                break;
            }

The thing is, I know that these texture coordinates are right. I've copied verbatim the coordinates and drawing code from probably a half-dozen code samples and tutorials I found on the web. That, combined with the fact that I can't find any set of texture coordinates that works, makes me thing I'm doing something terribly wrong somewhere else. I tried switching the winding order of the triangle vertices, and that had no visible effect. I also played with the blending functions with no success.

If there's anyone out there who's pretty good with OpenGL who can point out the boneheaded thing I'm doing here, I would really appreciate it. I think it's possible that it's the same thing that was keeping me from getting the UV-mapped OBJ files to display correctly.

If you're the first person to figure out what I'm doing wrong, you're welcome to a free copy of Beginning iPhone Development, though if you can figure this out, you've probably no need of it. Unfortunately, I can't afford to spend more time on this right now, so unless someone can figure this out, the particle tutorial is probably going to go on a shelf for a few weeks while I dig out from the Macworld backlog.

Better Template

Hello again.

I'm in desperate need of a better template for this blog - one that has good support for code snippets and preferably uses flexible width rather than just floating in the middle of the screen when the viewer has a large monitor (and these days, what developer doesn't?).

My searches for blogspot/blogger templates mostly brings up templates that have different visual elements, fonts, and colors, but the same basic layout as the default templates. If anyone knows of a good template, I'd really appreciate a heads up. I don't mind tweaking the code, but I don't have time write one from scratch. My Web-Fu is rusty and weak.

I've got a couple of more full-fledged tutorial I'm interested in doing, but it's just too painful with this template.

Thanks

Scroll Views

I've been realizing over the last couple of days that we missed covering something in the book that we should have: UIScrollView. Now that I've spent a few days fighting them, I must admit that I'm glad I missed it. These things are complex and not as well documented as they should be. I've got my app working with hit testing inside of a scroll view, and without jaggies, but my performance isn't good. Here's the thing:

UIScrollView ALWAYS starts at a zoom of 1.0. You can't change this. If you do, it will just cause it to act funny the first time the user touches the screen (please, if I'm wrong on this, correct me). But, if you zoom in on a view, it gets all pixelated and blocky unless you change your content view's (and/or subview's) backing layer to a CATiledLayer. Doing that kills performance on my first generation iPhone. I haven't tested it yet on my second generation iPod Touch, but I suspect it will only be a little bit better.

But, here's the thing. If I change the size so that I start zoomed in... so that the content view is the size of the zoomed view and don't use CATiledLayer, it works beautifully, scrolls fast, no skips, etc. But, I don't want the user to have to start zoomed way in. The program won't be intuitive if I do that.

A related problem is that I can't get the double-tap zoom and unzoom working. In an old edition of the iPhone Programming guide, there was sample code that supposedly showed how to do that, but I've tried it, and many, many variants of it, and never have gotten it to work right. There might be a reason why that code sample is no longer in the programming guide.

Anybody out there gotten this working?