Sign in to follow this  
purple_moon

OpenGL nonstandard texture sizes

Recommended Posts

purple_moon    122
It seems that both the width and height of an opengl texture must be a power of 2. But if I need to use a texture of nonstandard texture size, must I resize it or cut it into pieces?? I have once heard there are some ways around this limitation, is it true? If true ,what is it?? Thanks!!

Share this post


Link to post
Share on other sites
wendigo23    512
You can also load it into a texture of the next higher power of 2 size. Wasted space, but keeps your texels the same size if that's important to you. Keep in mind this won't work well if you need to tile the texture coords.

Share this post


Link to post
Share on other sites
purple_moon    122
Thank you a lot, bpoint & wendigo23!

It seems that wedingo23's idea fit me quite well, for I must keeps texels the same size . And I'm seldom need to tile the texture coords in my program.

Share this post


Link to post
Share on other sites
udaykv    126
Also, If I understand correctly, using tex coords in the range 0.0-1.0 won't give your correct results. Depending on your texture's aspect ratio and where within the texture you place your texels, you will have to adjust the tex coords on your polygons appropriately.

E.g. If you intend to store a 512x300 texture, the logical choice would be a 512x512 texture. Now, if you place your texture data in the upper part of your texture (which would generally be the case) the bottom 212 rows would still remain empty (white or garbage, the way you want them). So to correctly map the tex coords you need to map the t texcoord in the range (212.0/500.0, 1.0).

Share this post


Link to post
Share on other sites
Kalidor    1087
Quote:
Original post by bpoint
ARB_texture_non_power_of_two, if your card supports it (most do, nowadays).
Actually, GL_ARB_texture_non_power_of_two is not very widely supported yet. Out of NVIDIA and ATI only the GeForce 6x00 (and similar Quadro cards) and above support it. I'm not sure on the Radeon X1x00 cards but according to the OpenGL Extensions Viewer and Delphi3d's hardware list they don't. 3Dlabs' Wildcat Realizm and XGI's Volari Family cards apparently support it as well, but they are not very common in consumer PCs.

There is also GL_ARB_texture_rectangle which is more widely supported, but it has some other restrictions and differences over regular 2d textures. The main differences are...
 - Non-normalized texture coordinates ([0,w] x [0,h] instead of [0,1] x [0,1])
- No mipmapping
- Only clamping wrap modes
Read the spec for more information.

Share this post


Link to post
Share on other sites
wyled    127
I would advise against using any ARB extentions as they aren't supported by many cards.

Instead this issue can easily be resolved in your code instead of a quick (and sloppy) function fix.

Here is a function i wrote that can handle oddly sized textures, however you need to encase your textures in a data structure to remind your code of the initial size and the new size (it also handles PNG transparency):

(I appologize for the sloppyness of the code. It uses SDL_image to load images for compatibility and ease of use.

// in the .h file
typedef struct {
GLuint texture;
int ow; // Old width
int oh; // Old height
int w;
int h;
char filename[32];
char type;
char *bitmask;
} GLtexture;

// in the .c file
GLtexture* OGL_S2T(char *filename)
{

Uint8 *rowhi, *rowlo;
Uint8 *tmpbuf, tmpch;
SDL_Surface *s;
SDL_Surface *tmp;
int i, j;
int x2, y2;
SDL_Color clr;
Uint32 col = 0;
Uint32 col2 = 0;
char *gpos = NULL;
char *hpos = NULL;
int iw=0, ih=0;
int exp = 1;
GLtexture *tex = (GLtexture *)malloc(sizeof(GLtexture));

s = IMG_Load(filename);
if ( s == NULL ) {
fprintf(stderr, "Unable to load %s: %s\n", filename, SDL_GetError());
return(NULL);
}

SDL_DisplayFormatAlpha(s);
tex->ow = s->w;
tex->oh = s->h;

while(pow(2, exp) < s->w)
exp++;

iw = pow(2, exp);

exp = 1;

while(pow(2, exp) < s->h)
exp++;

ih = pow(2, exp);

tmp = SDL_CreateRGBSurface(SDL_HWSURFACE|SDL_SRCALPHA, iw, ih, 32, 0, 0, 0, 255);

SDL_LockSurface(tmp);
SDL_LockSurface(s);

y2 = 0;

while(y2 < s->h)
{
x2 = 0;
while(x2 < s->w)
{
gpos = (char *)s->pixels;
gpos += (s->pitch * y2);
gpos += (s->format->BytesPerPixel * x2);

hpos = (char*)tmp->pixels;
hpos += (tmp->pitch *y2);
hpos += (tmp->format->BytesPerPixel * x2);

memcpy(&col, gpos, s->format->BytesPerPixel);
SDL_GetRGBA(col, s->format, &clr.r, &clr.g, &clr.b, &clr.unused);
col2 = SDL_MapRGBA(s->format, clr.r, clr.g, clr.b, clr.unused);
memcpy(hpos, &col2, tmp->format->BytesPerPixel);

x2++;
}
y2++;
}
SDL_UnlockSurface(tmp);
SDL_UnlockSurface(s);

tex->bitmask = GenBitMask(s);

SDL_FreeSurface(s);

/* GL surfaces are upsidedown and RGB, not BGR :-) */
tmpbuf = (Uint8 *)malloc(tmp->pitch);
if ( tmpbuf == NULL ) {
fprintf(stderr, "Out of memory\n");
return(NULL);
}
rowhi = (Uint8 *)tmp->pixels;
rowlo = rowhi + (tmp->h * tmp->pitch) - tmp->pitch;
for ( i=0; i<tmp->h/2; ++i ) {
for ( j=0; j<tmp->w; ++j ) {
tmpch = rowhi[j*4];
rowhi[j*4] = rowhi[j*4+2];
rowhi[j*4+2] = tmpch;
tmpch = rowlo[j*4];
rowlo[j*4] = rowlo[j*4+2];
rowlo[j*4+2] = tmpch;
}
memcpy(tmpbuf, rowhi, tmp->pitch);
memcpy(rowhi, rowlo, tmp->pitch);
memcpy(rowlo, tmpbuf, tmp->pitch);
rowhi += tmp->pitch;
rowlo -= tmp->pitch;
}
free(tmpbuf);

glGenTextures(1, &tex->texture);
glBindTexture(GL_TEXTURE_2D, tex->texture);

tex->w = iw;
tex->h = ih;

glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);

glTexImage2D(GL_TEXTURE_2D, 0, 4, iw, ih, 0, GL_BGRA, GL_UNSIGNED_BYTE, tmp->pixels);

SDL_FreeSurface(tmp);

strcpy(tex->filename, filename);
tex->type = GFX_TYPE_BMP;

return tex;

}



Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Similar Content

    • By pseudomarvin
      I assumed that if a shader is computationally expensive then the execution is just slower. But running the following GLSL FS instead just crashes
      void main() { float x = 0; float y = 0; int sum = 0; for (float x = 0; x < 10; x += 0.00005) { for (float y = 0; y < 10; y += 0.00005) { sum++; } } fragColor = vec4(1, 1, 1 , 1.0); } with unhandled exception in nvoglv32.dll. Are there any hard limits on the number of steps/time that a shader can take before it is shut down? I was thinking about implementing some time intensive computation in shaders where it would take on the order of seconds to compute a frame, is that possible? Thanks.
    • By Arulbabu Donbosco
      There are studios selling applications which is just copying any 3Dgraphic content and regenerating into another new window. especially for CAVE Virtual reality experience. so that the user opens REvite or CAD or any other 3D applications and opens a model. then when the user selects the rendered window the VR application copies the 3D model information from the OpenGL window. 
      I got the clue that the VR application replaces the windows opengl32.dll file. how this is possible ... how can we copy the 3d content from the current OpenGL window.
      anyone, please help me .. how to go further... to create an application like VR CAVE. 
       
      Thanks
    • By cebugdev
      hi all,

      i am trying to build an OpenGL 2D GUI system, (yeah yeah, i know i should not be re inventing the wheel, but this is for educational and some other purpose only),
      i have built GUI system before using 2D systems such as that of HTML/JS canvas, but in 2D system, i can directly match a mouse coordinates to the actual graphic coordinates with additional computation for screen size/ratio/scale ofcourse.
      now i want to port it to OpenGL, i know that to render a 2D object in OpenGL we specify coordiantes in Clip space or use the orthographic projection, now heres what i need help about.
      1. what is the right way of rendering the GUI? is it thru drawing in clip space or switching to ortho projection?
      2. from screen coordinates (top left is 0,0 nd bottom right is width height), how can i map the mouse coordinates to OpenGL 2D so that mouse events such as button click works? In consideration ofcourse to the current screen/size dimension.
      3. when let say if the screen size/dimension is different, how to handle this? in my previous javascript 2D engine using canvas, i just have my working coordinates and then just perform the bitblk or copying my working canvas to screen canvas and scale the mouse coordinates from there, in OpenGL how to work on a multiple screen sizes (more like an OpenGL ES question).
      lastly, if you guys know any books, resources, links or tutorials that handle or discuss this, i found one with marekknows opengl game engine website but its not free,
      Just let me know. Did not have any luck finding resource in google for writing our own OpenGL GUI framework.
      IF there are no any available online, just let me know, what things do i need to look into for OpenGL and i will study them one by one to make it work.
      thank you, and looking forward to positive replies.
    • By fllwr0491
      I have a few beginner questions about tesselation that I really have no clue.
      The opengl wiki doesn't seem to talk anything about the details.
       
      What is the relationship between TCS layout out and TES layout in?
      How does the tesselator know how control points are organized?
          e.g. If TES input requests triangles, but TCS can output N vertices.
             What happens in this case?
      In this article,
      http://www.informit.com/articles/article.aspx?p=2120983
      the isoline example TCS out=4, but TES in=isoline.
      And gl_TessCoord is only a single one.
      So which ones are the control points?
      How are tesselator building primitives?
    • By Orella
      I've been developing a 2D Engine using SFML + ImGui.
      Here you can see an image
      The editor is rendered using ImGui and the scene window is a sf::RenderTexture where I draw the GameObjects and then is converted to ImGui::Image to render it in the editor.
      Now I need to create a 3D Engine during this year in my Bachelor Degree but using SDL2 + ImGui and I want to recreate what I did with the 2D Engine. 
      I've managed to render the editor like I did in the 2D Engine using this example that comes with ImGui. 
      3D Editor preview
      But I don't know how to create an equivalent of sf::RenderTexture in SDL2, so I can draw the 3D scene there and convert it to ImGui::Image to show it in the editor.
      If you can provide code will be better. And if you want me to provide any specific code tell me.
      Thanks!
  • Popular Now