如何使用OpenGL ES 1.1 for iPhone设置背景图像

Question

Please help me to set a background image in EaglView. Here my source code with the image:

    glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
            brushImage = [UIImage imageNamed:@"Particle.png"].CGImage;
    width = CGImageGetWidth(brushImage);
    height = CGImageGetHeight(brushImage);
    if(brushImage) {
        brushData = (GLubyte *) calloc(width * height * 4, sizeof(GLubyte));
        brushContext = CGBitmapContextCreate(brushData, width, height, 8, width * 4, CGImageGetColorSpace(brushImage), kCGImageAlphaPremultipliedLast);
        CGContextDrawImage(brushContext, CGRectMake(0.0, 0.0, (CGFloat)width, (CGFloat)height), brushImage);
        CGContextRelease(brushContext);
        glGenTextures(1, &brushTexture);
        glBindTexture(GL_TEXTURE_2D, brushTexture);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, brushData);
        free(brushData);
    }
    self.contentScaleFactor = 1.0;
    glLoadIdentity();
    glMatrixMode(GL_PROJECTION);
    CGRect frame = self.bounds;
    CGFloat scale = self.contentScaleFactor;
    glOrthof(0, frame.size.width * scale, 0, frame.size.height * scale, -1, 1);
    glViewport(0, 0, frame.size.width * scale, frame.size.height * scale);
    glMatrixMode(GL_MODELVIEW);
    glDisable(GL_DITHER);
    glEnable(GL_TEXTURE_2D);
    glEnableClientState(GL_VERTEX_ARRAY);
    glEnable(GL_BLEND);
    glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
    glEnable(GL_POINT_SPRITE_OES);
    glTexEnvf(GL_POINT_SPRITE_OES, GL_COORD_REPLACE_OES, GL_TRUE);
    glPointSize(width / kBrushScale);`

Answer 1

Instead of using a point sprite should simply draw a textured quad.

GLfloat vert_tex[] = {
    0., 0.,
    1., 0.,
    1., 1.,
    0., 1.
};

glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glVertexPointer(2, GL_FLOAT, 0, vert_tex);
glTexCoordPointer(2, GL_FLOAT, 0, vert_tex);

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, 1, 0, 1, -1, 1);

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture_name);

glDrawArrays(GL_QUADS, 0, 4);

EDIT2:

// Erases the screen
- (void) erase
{
    [EAGLContext setCurrentContext:context];

    CGRect frame = self.bounds;
    CGFloat scale = self.contentScaleFactor;

    GLfloat vert_tex[] = {
        0., 0.,
        frame.size.width * scale, 0.,
        frame.size.width * scale, frame.size.height * scale,
        0., frame.size.height * scale
    };

    glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);

    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);
    glVertexPointer(2, GL_FLOAT, 0, vert_tex);
    glTexCoordPointer(2, GL_FLOAT, 0, vert_tex);

    // Setup the view port in Pixels
    glMatrixMode(GL_PROJECTION);
    glOrthof(0, frame.size.width * scale, 0, frame.size.height * scale, -1, 1);
    glViewport(0, 0, frame.size.width * scale, frame.size.height * scale);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glDisable(GL_DITHER);    
    glEnable(GL_TEXTURE_2D);

    // background_image texture must be initialized with the desired
    // content; see initWithCoder of original GLPaint example for
    // example code how to load textures.
    glBindTexture(GL_TEXTURE_2D, background_image);

    // Clear the buffer with background image    
    glDrawArrays(GL_QUADS, 0, 4);

    // Display the buffer
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
    [context presentRenderbuffer:GL_RENDERBUFFER_OES];

}

In renderLineFromPoint you must add a line to bind the brush texture before drawing:

// Drawings a line onscreen based on where the user touches
- (void) renderLineFromPoint:(CGPoint)start toPoint:(CGPoint)end
{
     /* ... */


     // add this line here v v v v v v v v v v v
     glBindTexture(GL_TEXURE_2D, brushTexture);
     // ^ ^ ^ ^^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^

     // Render the vertex array
     glVertexPointer(2, GL_FLOAT, 0, vertexBuffer);
     glDrawArrays(GL_POINTS, 0, vertexCount);

     // Display the buffer
     glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
     [context presentRenderbuffer:GL_RENDERBUFFER_OES];