Displaying image with OpenGL and DevIL in C?

Displaying image with OpenGL and DevIL in C? - Printable Version

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Displaying image with OpenGL and DevIL in C? - leRiCl - Jan 21, 2007 09:49 PM

how to display image with OpenGL and DevIL? Or is this not possible, and I must use libs like libPNG instead?

Code:

ilutGLLoadImage("/Users/eric/GLExperiment/Images/fighter.png");

glDrawPixels(64,64,GL_RGB,GL_UNSIGNED_BYTE,ilGetData);

This code doesn't do anything. Not surprisingly..

and then I tried using textures...

Code:

ilutGLLoadImage("/Users/eric/GLExperiment/Images/fighter.png");

    ilGenImages (1, &ImgId);

    ilBindImage (ImgId);

glEnable (GL_TEXTURE_2D);

    glBindTexture (GL_TEXTURE_2D, TexID);

    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);

    glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

    glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);

    glTexImage2D (GL_TEXTURE_2D, 0, GL_RGB, Width, Height, 0, GL_RGB, GL_UNSIGNED_BYTE, ilGetData);

    glBegin (GL_QUADS);

    glTexCoord2f (X1, Y1);// glVertex3i (0,     0,      0);

    glVertex2f(X1, Y1);

    glTexCoord2f (X1+Width,Y1);// glVertex3i (Width, 0,      0);

    glVertex2f(X1+Width, Y1); 

    glTexCoord2f (X1+Width,Y1+Height);// glVertex3i (Width, Height, 0);

    glVertex2f(X1+Width,  Y1+Height);

    glTexCoord2f (X1, Y1+Height);// glVertex3i (0,     Height, 0);

    glVertex2f(X1,Y1+Height);

    glEnd();

This code manages to turn every shape's colour in the screen to the most predominant colour in the image. I was trying to do it with textures.

Displaying image with OpenGL and DevIL in C? - akb825 - Jan 21, 2007 09:58 PM

The texture coordinates should go from 0 to 1. So where you have glTexCoord2f(X1, Y1), you should have glTexCoord2f(0, 0). Also, in place of glVertex2f(X1 + Width, Y1 + Height), you should have glVertex2f(1, 1). I'm sure you can figure out the rest.

Displaying image with OpenGL and DevIL in C? - OneSadCookie - Jan 22, 2007 01:17 AM

and I'm sure ilGetData is a function, not a global variable!

Displaying image with OpenGL and DevIL in C? - leRiCl - Jan 22, 2007 03:51 AM

akb825 Wrote:The texture coordinates should go from 0 to 1. So where you have glTexCoord2f(X1, Y1), you should have glTexCoord2f(0, 0). Also, in place of glVertex2f(X1 + Width, Y1 + Height), you should have glVertex2f(1, 1). I'm sure you can figure out the rest.

I did that thing OneSadCookie told me in his tutorial. -> make the coordinate system measure interms of pixels instead of the default system. I still use the coordinates you told me

OneSadCookie Wrote:and I'm sure ilGetData is a function, not a global variable!

Its a function, I can use it like this, right? It gets the memory address of the image I loaded, and returns it as a pointer.

Displaying image with OpenGL and DevIL in C? - OneSadCookie - Jan 22, 2007 03:57 AM

Function calls in C always have parentheses.

Displaying image with OpenGL and DevIL in C? - leRiCl - Jan 22, 2007 04:24 AM

OneSadCookie Wrote:Function calls in C always have parentheses.

>.> Why didn't it give me an error?

Displaying image with OpenGL and DevIL in C? - OneSadCookie - Jan 22, 2007 04:29 AM

In C, you can pass any kind of pointer as a void*. You were passing a function pointer.

Displaying image with OpenGL and DevIL in C? - leRiCl - Jan 22, 2007 04:31 AM

I put the parenthesis in, now all the rectangles and lines on my app flash green blue and red, make my head dizzy.. >< But I still don't see any image! Note that I am able to get data about the image, eg. its width and height, so I am sure I have it loaded into the app.

Code:

'see other posts. deleted for space.

Displaying image with OpenGL and DevIL in C? - akb825 - Jan 22, 2007 11:38 AM

You still haven't changed the texture coordinates. Having the coordinate system match up pixel by pixel works with the vertex coordinates, but not the texture coordinates. Like I said earlier, they go from 0 to 1: always. (unless you are using GL_TEXTURE_RECTANGLE_EXT/ARB instead of GL_TEXTURE_2D, but that's the only exception) Also, you can't just say "TexID = 2". You have to call glGenTextures first.

Displaying image with OpenGL and DevIL in C? - OneSadCookie - Jan 22, 2007 01:45 PM

akb825 Wrote:Also, you can't just say "TexID = 2". You have to call glGenTextures first.

Unfortunately, you're wrong about that. You *can* choose your own texture IDs, and OpenGL just has to deal. This is something that they will fix for OpenGL LM / OpenGL 3.0. You're right, though, that you *should* call GenTextures.

leRiCi, isn't there a DevIL function that does the TexImage2D for you?

Displaying image with OpenGL and DevIL in C? - leRiCl - Jan 22, 2007 03:43 PM

There is, but the example containing the command won't compile. Anyways... I realised I posted the wrong version of the code I had. Here, I called GenTextures and didn't declare my TexID and changed the texture coordinates and used the GL command for DevIL. Now it doesn't do anything at all. ><

Code:

// GL texture ID

GLuint TexID;

// IL image ID

ILuint ImgId;

ILboolean success;

    ilGenImages (1, &ImgId);

    ilBindImage (ImgId);

    success = ilLoadImage("/Users/eric/GLExperiment/Images/fighter.png");

    if (success)

    {

    success= ilConvertImage(IL_RGB,IL_UNSIGNED_BYTE);

    if (!success)

    {

    }

    glGenTextures(1, &TexID);

     glBindTexture(GL_TEXTURE_2D, TexID);

     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); /* We will use linear

      interpolation for magnification filter */

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); /* We will use linear

      interpolation for minifying filter */

    glTexImage2D(GL_TEXTURE_2D, 0, ilGetInteger(IL_IMAGE_BPP), ilGetInteger(IL_IMAGE_WIDTH),

      ilGetInteger(IL_IMAGE_HEIGHT), 0, ilGetInteger(IL_IMAGE_FORMAT), GL_UNSIGNED_BYTE,

      ilGetData()); /* Texture specification */

      }

      else

      {

      }

      int Width  = ilGetInteger (IL_IMAGE_WIDTH);

    int    Height = ilGetInteger (IL_IMAGE_HEIGHT);

      glBegin(GL_QUADS);

    glTexCoord2i(0, 0); glVertex2i(X1,   Y1);

    glTexCoord2i(0, 1); glVertex2i(X1,   Y1+Height);

    glTexCoord2i(1, 1); glVertex2i(X1+Width, Y1+Height);

    glTexCoord2i(1, 0); glVertex2i(X1+Width, Y1);

    glEnd();

Displaying image with OpenGL and DevIL in C? - akb825 - Jan 22, 2007 04:29 PM

What's the value of X1 and Y1? Are you trying to give the value of the window's x and y? If so, don't. Assuming you correctly set up the orthographic matrix (for example, with glOrtho(0, width, 0, height, 1, -1)) and viewport (for example, glViewport(0, 0, width, height)), the viewable coordinates should be 0-width for the x and 0-height for the y.

Displaying image with OpenGL and DevIL in C? - leRiCl - Jan 22, 2007 04:36 PM

I want to put my head in the toilet and flush it away.... I called this function before glClear.... *sigh* It probably had always been working, and I was just wasting my time. Sorry guys. but thanks.

Displaying image with OpenGL and DevIL in C? - djork - Jan 23, 2007 01:25 PM

leRiCl Wrote:I want to put my head in the toilet and flush it away.... I called this function before glClear.... *sigh* It probably had always been working, and I was just wasting my time. Sorry guys. but thanks.

No sweat. I did the same thing yesterday. I was pulling my hair out trying to figure out why my screen was blank.