Problem with opengles to show an image - iphone

Question

I use xcode Opengl App template to create a sample.
I am new to opengles, and having to try re-write the 'render' method in ES1Renderer.m
I try create a texture and show it on the screen, but nothing showed.
Someone can help me ? I have no idea how to fix it:
- (void)render
{
int imageW = 16;
int imageH = 16;
GLubyte *textureData = (GLubyte *) malloc(imageW * imageH << 2);
for (int i = 0; i < imageW * imageH << 2; i++) {
textureData[i]= 0xff & i;
}
GLuint textureId;
glGenTextures(1, &textureId);
glBindTexture(GL_TEXTURE_2D, textureId);
// when texture area is small, bilinear filter the closest mipmap
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
GL_LINEAR );
// when texture area is large, bilinear filter the original
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
// the texture wraps over at the edges (repeat)
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, imageW, imageH, 0, GL_RGBA, GL_UNSIGNED_BYTE, textureData);
GLenum err = glGetError();
if (err != GL_NO_ERROR)
NSLog(#"Error uploading texture. glError: 0x%04X", err);
free(textureData);
float x = 10.0f;
float y = 10.0f;
float z = 0.0f;
float scaleX = 1.0f;
float scaleY = 1.0f;
float scaleZ = 1.0f;
int w = imageW /2;
int h = imageH /2;
const GLfloat squareVertices[] = {
-w, -h,
w, -h,
-w, h,
w, h,
};
const GLfloat textureCoords[] = {
0, 0,
1, 0,
0, 1,
1, 1,
};
glEnable(GL_TEXTURE_2D);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glEnableClientState(GL_VERTEX_ARRAY);
glBindTexture(GL_TEXTURE_2D, textureId);
glVertexPointer(2, GL_FLOAT, 0, squareVertices);
glTexCoordPointer(2, GL_FLOAT, 0, textureCoords);
glPushMatrix();
glTranslatef(x, y, z);
glScalef(scaleX, scaleY, scaleZ);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glPopMatrix();
glDisable(GL_TEXTURE_2D);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glDisableClientState(GL_VERTEX_ARRAY);
NSLog(#"-->");
glDeleteTextures(1, &textureId);
// This application only creates a single color renderbuffer which is already bound at this point.
// This call is redundant, but needed if dealing with multiple renderbuffers.
glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER_OES];
}

Answer 1

Sadly the OpenGL template provided by Xcode has changed at some point — the current code (as of Xcode 3.2.5, creating an iOS Application with the 'OpenGL ES Application' template) no longer supplies a separate ES1Renderer.m and ES2Renderer.m, preferring to provide a single, simplified EAGLView.m and to perform runtime tests within GLTestViewController.m. With that in mind, I modified GLTestViewController.m's awakeFromNib no longer to attempt to get an ES 2 context:
- (void)awakeFromNib
{
EAGLContext *aContext = nil;//[[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
if (!aContext)
{
aContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES1];
}
if (!aContext)
NSLog(#"Failed to create ES context");
else if (![EAGLContext setCurrentContext:aContext])
NSLog(#"Failed to set ES context current");
self.context = aContext;
[aContext release];
[(EAGLView *)self.view setContext:context];
[(EAGLView *)self.view setFramebuffer];
if ([context API] == kEAGLRenderingAPIOpenGLES2)
[self loadShaders];
animating = FALSE;
animationFrameInterval = 1;
self.displayLink = nil;
}
And copied and pasted relevant portions of your code into drawFrame:
- (void)drawFrame
{
[(EAGLView *)self.view setFramebuffer];
// Replace the implementation of this method to do your own custom drawing.
static const GLfloat squareVertices[] = {
-0.5f, -0.33f,
0.5f, -0.33f,
-0.5f, 0.33f,
0.5f, 0.33f,
};
const GLfloat textureCoords[] = {
0, 0,
1, 0,
0, 1,
1, 1,
};
static float transY = 0.0f;
glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
int imageW = 16;
int imageH = 16;
GLubyte *textureData = (GLubyte *) malloc(imageW * imageH << 2);
for (int i = 0; i < imageW * imageH << 2; i++) {
textureData[i]= 0xff & i;
}
GLuint textureId;
glGenTextures(1, &textureId);
glBindTexture(GL_TEXTURE_2D, textureId);
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, imageW, imageH, 0, GL_RGBA, GL_UNSIGNED_BYTE, textureData);
free(textureData);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0f, (GLfloat)(sinf(transY)/2.0f), 0.0f);
transY += 0.075f;
glEnable(GL_TEXTURE_2D);
glVertexPointer(2, GL_FLOAT, 0, squareVertices);
glEnableClientState(GL_VERTEX_ARRAY);
glTexCoordPointer(2, GL_FLOAT, 0, textureCoords);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glDeleteTextures(1, &textureId);
[(EAGLView *)self.view presentFramebuffer];
}
The result works entirely as you seem to intend. At a guess, is it possible either that:
you're setting something other than the identity as your projection matrix, causing your geometry to be clipped because it is placed at z = 0?
you've neglected properly to abandon an attempt at ES 2 rendering, causing unexpected results because tasks like textured rendering aren't hardwired in with ES 2 in the same way that they are with ES1?