loading textures with SDL
November 11, 2004 11:45 AM
I load textures using SDL and now want to use the alpha channel in PNGs.
Does any one know how to do this?
Currently if I try to load a PNG with an Alpha channel the entire texture is transparent.
Thanks
122
November 11, 2004 12:32 PM
question,
are you using OpenGL in a SDL context or are you strictly using the SDL.lib and SDL_Image.lib
are you using OpenGL in a SDL context or are you strictly using the SDL.lib and SDL_Image.lib
Hard work USUALLY pays off in the future, but laziness ALWAYS pays off right now.
November 11, 2004 12:52 PM
I am using SDL.lib and SDL_Image.lib to load the images
122
November 11, 2004 12:56 PM
gotcha, but are you using OpenGL commands to display the images or are you using SDL commands to display the images?
Hard work USUALLY pays off in the future, but laziness ALWAYS pays off right now.
November 11, 2004 01:08 PM
I use SDL to load a surface then convert the surface into a openGL texture which is then applied to a plain, again in opengl.
Opengl does all the rendering and SDL does the file and windows handling.
Opengl does all the rendering and SDL does the file and windows handling.
122
November 11, 2004 08:43 PM
GLuint g_texture[MAX_TEXTURES];
SDL_Surface *image;
SDL_RWops *rwop;
rwop=SDL_RWFromFile("sample.png", "rb");
image=IMG_LoadPNG_RW(rwop);
glGenTextures(1, &texture);
glPixelStorei (GL_UNPACK_ALIGNMENT, 1);
glBindTexture(GL_TEXTURE_2D, g_texture[next_number_goes_here]);
gluBuild2DMipmaps(GL_TEXTURE_2D, 4, image->w,image->h,GL_RGBA, GL_UNSIGNED_BYTE, image->pixels);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
This should correctly create your OpenGL texture from a PNG file using SDL_Image.lib
Then, to draw with alpha blending enabled,
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, g_texture[the one you loaded]);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
glBegin(whatever you need);
// repeat following as necessary
glTexCoord2f(input vertex u,v coords here);
glVertex3f(input vertex x,y,z coords here);
//
glEnd();
glDisable(GL_BLEND);
glDisable(GL_TEXTURE_2D);
hope that helps and I dinnae have any typos...
SDL_Surface *image;
SDL_RWops *rwop;
rwop=SDL_RWFromFile("sample.png", "rb");
image=IMG_LoadPNG_RW(rwop);
glGenTextures(1, &texture);
glPixelStorei (GL_UNPACK_ALIGNMENT, 1);
glBindTexture(GL_TEXTURE_2D, g_texture[next_number_goes_here]);
gluBuild2DMipmaps(GL_TEXTURE_2D, 4, image->w,image->h,GL_RGBA, GL_UNSIGNED_BYTE, image->pixels);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
This should correctly create your OpenGL texture from a PNG file using SDL_Image.lib
Then, to draw with alpha blending enabled,
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, g_texture[the one you loaded]);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
glBegin(whatever you need);
// repeat following as necessary
glTexCoord2f(input vertex u,v coords here);
glVertex3f(input vertex x,y,z coords here);
//
glEnd();
glDisable(GL_BLEND);
glDisable(GL_TEXTURE_2D);
hope that helps and I dinnae have any typos...
Hard work USUALLY pays off in the future, but laziness ALWAYS pays off right now.
November 12, 2004 01:37 AM
That looks almost identical to my code only I dont know what glPixelStorei (GL_UNPACK_ALIGNMENT, 1);
and
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE); are about
I perhaps should state that I currently have no problems loading pngs if they have no alpha transparent parts.
I will try your suggestion.
Thanks
and
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE); are about
I perhaps should state that I currently have no problems loading pngs if they have no alpha transparent parts.
I will try your suggestion.
Thanks
November 12, 2004 04:09 PM
My stupid
I can show png's with transparent parts but the transparent part shows as black can anyone help with this?
I can show png's with transparent parts but the transparent part shows as black can anyone help with this?
122
November 12, 2004 09:02 PM
traiger,
post your "render scene" code for the section where you are trying to draw the .png
Mebbe that will help me understand better, thanks
post your "render scene" code for the section where you are trying to draw the .png
Mebbe that will help me understand better, thanks
Hard work USUALLY pays off in the future, but laziness ALWAYS pays off right now.
November 13, 2004 02:25 AM
This part of the engine makes a texture from a pre loaded surface called BM->Bitmap
void stDB_Images::Get_Image(class stDBBitmaps *BM, GLuint x, GLuint y, GLuint w, GLuint h){ GLuint old_texture=texture; SDL_Surface *image; SDL_Rect Dest_Rect; /* Use the surface width and height expanded to powers of 2 */ o_width = w; o_height = h; Dest_Rect.w = o_width; Dest_Rect.h = o_height; width = power_of_two(w); height = power_of_two(h); Dest_Rect.x = (width/2)-o_width/2; Dest_Rect.y = (height/2)-o_height/2; x_offset = Dest_Rect.x; y_offset = Dest_Rect.y; image = SDL_CreateRGBSurface(SDL_SWSURFACE, width, height,32,#if SDL_BYTEORDER == SDL_LIL_ENDIAN /* OpenGL RGBA masks */ 0x000000FF, 0x0000FF00, 0x00FF0000, 0xFF000000#else 0xFF000000, 0x00FF0000, 0x0000FF00, 0x000000FF#endif ); /* Copy the surface GLuinto the GL texture image */ area.x = x; area.y = y; area.w = w; area.h = h; SDL_BlitSurface(BM->Bitmap, &area, image, &Dest_Rect); /* Create an OpenGL texture for the image */ glGenTextures(1, &texture); glBindTexture(GL_TEXTURE_2D, texture); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height,0, GL_RGBA, GL_UNSIGNED_BYTE,image->pixels); SDL_FreeSurface(image); /* No longer needed */}This part renders the sprite only showing the first part here which renders sprites smaller than 256x256
void stDB_Sprite::Draw(void){ glTranslated(this->x_translate,this->y_translate,0); glRotated((GLdouble)this->rotatez,0,0,1); glTranslated((-(this->x_translate)+this->x),(-(this->y_translate))+this->y,this->z); glBlendFunc(sf, df) ; glMatrixMode(GL_TEXTURE); glLoadIdentity(); glTranslated(0.5f,0.5f,0); glRotated(this->texture_rotatez,0,0,1); glTranslated(-0.5f,-0.5f,0); glMatrixMode(GL_MODELVIEW); glBindTexture(GL_TEXTURE_2D, this->texture); if(this->img_w<=256 && this->img_h<=256) { glBegin(GL_QUADS); //bl glColor4d(bl.r, bl.g, bl.b,this->alpha); glTexCoord2d(0,1); glVertex2d( 0, this->img_h*y_scale); //br glColor4d(br.r,br.g,br.b,this->alpha); glTexCoord2d(1,1); glVertex2d(this->img_w*x_scale, this->img_h*y_scale); //tr glColor4d(tr.r,tr.g,tr.b,this->alpha); glTexCoord2d(1,0); glVertex2d( this->img_w*x_scale,0); //tl glColor4d(tl.r,tl.g,tl.b,this->alpha); glTexCoord2d(0,0); glVertex2d(0,0); glEnd(); }This topic is closed to new replies.
Advertisement
Popular Topics
Advertisement
