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Texture Loading

Started by Imaginate Apr 15, 2006 at 2:51 AM 1 reply 750+ views

Original Post

Apr 15, 2006 at 2:51 AM

Hi there, I'm developing a 2D Game Engine, which is currently using GDI to draw, but I want to use OpenGL. So far, I've been sucessful in drawing shapes to the screen ( by adding code to my engine's GDI-based functions that replaces GDI calls with OpenGL calls ), and I've come to the point where I need to precache an image. I know how to precache images as textures, but the thing is, the images aren't always precached at once. The GDI version simply retrieves an HBITMAP and places it within a vector, so it can be drawn by giving a supplied handle. However, if I'm not mistaken, OpenGL wants me to precache all textures at once, after calling glGenTextures or something of the sort. I can't do this, as it would destroy the engine's functionality. The current GDI function loads in the image to an IPicture, then into a DDB HBITMAP, which is stored in a vector, and then the drawing function cross-references the handle with another vector of handles, which allows the drawing function to access the HBITMAP. Using OpenGL, how can I have the precaching function work without destroying already precached images ( since images can be precached at anytime by the client-game ) ? Thanks, The Imaginate

Kalidor

Apr 17, 2006 at 12:14 PM

Quote:
Original post by Imaginate
...
However, if I'm not mistaken, OpenGL wants me to precache all textures at once, after calling glGenTextures or something of the sort.
...

You are mistaken. OpenGL has no such restriction on when you create textures; as long as there is a current valid rendering context you can create a texture pretty much whenever you want.

falledAngel

Apr 17, 2006 at 12:27 PM

GLuint textura[1];

AUX_RGBImageRec *LoadBMP(char *nomFitxer) {
FILE *File = NULL;
if (!nomFitxer) {
return NULL;
}
File=fopen(nomFitxer,"r");
if (File) {
fclose(File);
return auxDIBImageLoad(nomFitxer);
}
return NULL;
}

int LoadGLTextures() {
int Status = FALSE;
AUX_RGBImageRec *TextureImage[1];
memset(TextureImage, 0, sizeof(void *)*1);
if (TextureImage[0]=LoadBMP("pathFile")) {
Status = TRUE;
glGenTextures(1, &textura[0]);
glBindTexture(GL_TEXTURE_2D, textura[0]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
gluBuild2DMipmaps(GL_TEXTURE_2D, 3, TextureImage[0]->sizeX, TextureImage[0]->sizeY, GL_RGB, GL_UNSIGNED_BYTE, TextureImage[0]->data);

}
if (TextureImage[0]) {
if (TextureImage[0]->data) {
free(TextureImage[0]->data);
}
}
return Status;
}

I Hope this can help you.

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