Question

Loading an image using texture in OpenGL

Asked by: zivf


Hi!
I'm trying to load an image onto my opengl scene.
i've created a shape, and used texture to load the image onto that shape.

Follows is my setupView function (which is called by initWithCode:)


The problem is, when i load my texture, i have to guess the size of the shape (for my 256x256,  so it will be a power-of-2 size) image, i use the size: 1.58.
Anyone knows how could i do this pixel-to-pixel, meaning: 2.56 (256 pixels) would be the size i would have to enter?

thanks.

(void)setupView {
  
    const GLfloat zNear = 0.01, zFar = 10000.0;
    GLfloat size;
  
    glEnable(GL_DEPTH_TEST);
    glMatrixMode(GL_PROJECTION);
    size=1.0;
  
    // This give us the size of the iPhone display
    CGRect rect = self.bounds;
    glOrthof(-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);
  
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
}

                                  
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Asked On
2009-08-20 at 01:55:44ID24667439
Tags

opengl

,

image loading

,

opengl ef

,

iphone

,

objective c

Topics

OpenGL Graphics & Game Programming

,

3D Game Programming

,

Game Programming User Interface

Participating Experts
2
Points
500
Comments
3

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Answers

 

by: ikeworkPosted on 2009-08-20 at 05:07:55ID: 25141390

Hi zivf

>> when i load my texture, i have to guess the size of the shape

You dont have to guess, you can read it from the file.


>> i use the size: 1.58.
>> Anyone knows how could i do this pixel-to-pixel, meaning: 2.56 (256 pixels) would be the size i would have to enter?

What you mean by that. Where do you use "1.58"? Where do you want to enter it?


ike

 

by: JoseParrotPosted on 2009-08-23 at 00:37:36ID: 25161672

In general, we don't determine the 1:1 relationship for pixel in the image file and pixel in the screen, due the difficult to guarantee the harmony between the image size, the viewport size, the screen size, the screen factor, the aspect ratio and so on.

As you are using ortho projection, you can adjust the viewport to have the same size, in pixels, as the image you load. If you have success, should notice that it is correct for such environment, say, other computers can have different results.

The "sizes" you reffer to are to determine how many times the texture shoud be applied to the surface, in both x and y directions.

Please note, OpenGL is not intended for image processing (although has capabiliotis to do it), but for 2D and 3D geometric objects projection and rendering.

Jose

 

by: zivfPosted on 2009-08-23 at 03:11:50ID: 31618048

thanks, I found the solution

20120131-EE-VQP-002

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