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krikit
04-10-2012, 01:54 AM
Hello everybody,

i have a little problem to read my pixels back from the GPU. I use the following code element.


-(void)readPixels : (unsigned char*) image pictureDest: (unsigned char*) dest
{
static const GLfloat textureVertices[] =
{
0.0f, 1.0f,
0.0f, 0.0f,
1.0f, 1.0f,
1.0f, 0.0f,
};

static const GLfloat squareVertices[] =
{
-1.0f, -1.0f,
1.0f, -1.0f,
-1.0f, 1.0f,
1.0f, 1.0f
};

glGenTextures(1, &pictureTexture);
glActiveTexture(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, pictureTexture);

glUniform1i(uniforms[UNIFORM_VIDEOFRAME], 0);

glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, 0, 0, squareVertices);
glEnableVertexAttribArray(ATTRIB_VERTEX);
glVertexAttribPointer(ATTRIB_TEXTUREPOSITON, 2, GL_FLOAT, 0, 0, textureVertices);
glEnableVertexAttribArray(ATTRIB_TEXTUREPOSITON);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, imageHeight, imageWidth, 0, GL_RGBA, GL_UNSIGNED_BYTE, image);

glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glViewport(0, 0, imageHeight, imageWidth);

[self presentFramebuffer];

glReadPixels(0, 0, imageHeight, imageWidth, GL_RGBA, GL_UNSIGNED_BYTE, dest);

glDeleteTextures(1, &pictureTexture);
}

I call this method with the same data element as source and destination and show it on the screen. But i got a picture from glReadPixels() which is much smaller then the original image. There is a bar on the right side with the original pixels from the source image).

Can someone help me with this problem?

Greets
krikit

krikit
04-19-2012, 12:26 AM
Hello,

i found my mistake. The initialization of the view was wrong. I used a rectangle with a size which was too small to render the complete image.

So i tried to change the rectangle size and everything works fine.


_instance = [super initWithFrame:CGRectMake(0.0f, 0.0f, 2000, 2860)];


In the wrong case i've initialized the rectangle with the application.frame.size.width / height which was too small.

best regards
krikit