c++ - Scaling a texture with a Framebuffer -

my goal able scale textures when loaded, don't have on every frame sprite gets rendered. figured best method render scaled texture onto texture, caching it. however, following code, red quads (due glclearcolor) know fbo working, not method rendering new texture

texture *graphics::loadtexture(const std::string& filename, int scale = 0) { sdl_surface *surface; gluint texture;  if((surface = img_load(filename.c_str()))) {     // number of colors     glint numberofcolors = surface->format->bytesperpixel;     glenum format;      // set format of texture based on number of channels     if(numberofcolors == 4) {             if(surface->format->rmask == 0x000000ff) {                 format = gl_rgba;             } else {                 format = gl_bgra;             }     } else if(numberofcolors == 3) {         if(surface->format->rmask == 0x000000ff) {             format = gl_rgb;         } else {             format = gl_bgr;         }     } else {         throw exception("invalid image type image  " + filename);      }      // generate texture id     glgentextures(1, &texture);      // bind texture     glbindtexture(gl_texture_2d, texture);      // texture stretching properties     gltexparameteri(gl_texture_2d, gl_texture_min_filter, gl_nearest);     gltexparameteri(gl_texture_2d, gl_texture_mag_filter, gl_nearest);      // create image     glteximage2d(gl_texture_2d, 0, 4, surface->w, surface->h,                  0, format, gl_unsigned_byte, surface->pixels);      glbindtexture(gl_texture_2d, 0);  } else {     return null; } texture *result;  if(scale > 1) {     gluint scaledtexture;     gluint fbo;     gluint fbod;      // first setup depth buffer //     // create framebuffer     glgenrenderbuffersext(1, &fbod);      // bind render buffer     glbindrenderbufferext(gl_renderbuffer_ext, fbod);      // set render buffer storage depth component     glrenderbufferstorageext(gl_renderbuffer_ext, gl_depth_component, surface->w*scale, surface->h*scale);      // set render buffer of buffer depth buffer     glframebufferrenderbufferext(gl_framebuffer_ext, gl_depth_attachment_ext, gl_renderbuffer_ext, fbod);      // unbind render buffer     glbindrenderbufferext(gl_renderbuffer_ext, 0);      // next setup texture //     glgentextures(1, &scaledtexture);     glbindtexture(gl_texture_2d, scaledtexture);     glteximage2d(gl_texture_2d, 0, gl_rgba, surface->w*scale, surface->h*scale, 0, gl_rgba, gl_unsigned_byte, null);      gltexparameterf(gl_texture_2d, gl_texture_wrap_s, gl_clamp_to_edge);     gltexparameterf(gl_texture_2d, gl_texture_wrap_t, gl_clamp_to_edge);     gltexparameterf(gl_texture_2d, gl_texture_mag_filter, gl_linear);     gltexparameterf(gl_texture_2d, gl_texture_min_filter, gl_linear);      glbindtexture(gl_texture_2d, 0);      // setup frame buffer //     glgenframebuffersext(1, &fbo);     glbindframebufferext(gl_framebuffer_ext, fbo);      // attach texture , render buffer frame buffer     glframebuffertexture2dext(gl_framebuffer_ext, gl_color_attachment0_ext, gl_texture_2d,  scaledtexture, 0);      // attach depth buffer     glframebufferrenderbufferext(gl_framebuffer_ext, gl_depth_attachment_ext, gl_renderbuffer_ext, fbod);      glpushattrib(gl_viewport_bit | gl_enable_bit);     glviewport(0, 0, surface->w*scale, surface->h*scale);      glloadidentity();      glclearcolor(1.0f, 0.0f, 0.0f, 1.0f);     glclear(gl_color_buffer_bit | gl_depth_buffer_bit);      glbindtexture(gl_texture_2d, texture);      glpushmatrix();      glbegin(gl_quads);         gltexcoord2i( 0, 0 );         glvertex3f( 0.f, 0.f, 0.0f );          gltexcoord2i( 1, 0 );         glvertex3f( (glfloat)surface->w*scale, 0.0f, 0.0f );          gltexcoord2i( 1, 1 );         glvertex3f( (glfloat)surface->w*scale, (glfloat)surface->h*scale, 0.f );          gltexcoord2i( 0, 1 );         glvertex3f( 0.0f, (glfloat)surface->h*scale, 0.f );     glend();      glpopmatrix();       glclearcolor(0.0f, 0.0f, 0.0f, 1.0f);      glpopattrib();     glbindframebufferext(gl_framebuffer_ext, 0);      result = new texture(scaledtexture, surface->w, surface->h); } else {     result = new texture(texture, surface->w, surface->h); }  //texture *result = new texture(texture, surface->w, surface->h);  if(surface) {     sdl_freesurface(surface); }  return result; } 

several comments :

• when glloadidentity(), know matrix resetting ? use glmatrixmode.
• your glpushmatrix()/glpopmatrix() useless since don't modify matrix inbetween.
• are sure 2d textures enabled ? use glenable(gl_texture_2d);

but anyway, clear both matrices , should see texture in upper right part of screen (or whatever polygon on you're using generated texture) ; you'll have fix uvs et graphics::loadtexture :

glmatrixmode(gl_modelview); glloadidentity(); glmatrixmode(gl_projection); glloadidentity(); 

this should work, think should scaling in software.