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POHow to properly use SDL_BlitSurface() with SDL_CreateRGBSurface()?
 

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  1. POHow to properly use SDL_BlitSurface() with SDL_CreateRGBSurface()?
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    <p>(See "Edit 2" below for the solution.)</p> <p>I need to create SDL surfaces from scratch, instead of loading them from a file. Unfortunately, <code>SDL_BlitSurface()</code> seems to render all colors as black when used with the surface generated through <code>SDL_CreateRGBSurface()</code>. This is my code:</p> <pre><code>int main(int argc, char** argv) { SDL_Surface* screen = SDL_SetVideoMode(640, 480, 32, SDL_HWSURFACE); SDL_Surface* layer = SDL_CreateRGBSurface(SDL_HWSURFACE, 100, 100, screen-&gt;format-&gt;BitsPerPixel, screen-&gt;format-&gt;Rmask, screen-&gt;format-&gt;Gmask, screen-&gt;format-&gt;Bmask, screen-&gt;format-&gt;Amask ); SDL_Rect rect; rect.x = 0; rect.y = 0; rect.w = 100; rect.h = 100; Uint32 blue = SDL_MapRGB(screen-&gt;format, 0, 0, 255); SDL_FillRect(layer, &amp;rect, blue); SDL_BlitSurface(screen, NULL, layer, NULL); SDL_Flip(screen); SDL_Delay(3000); return 0; } </code></pre> <p>What I get is a black screen, instead of a 100x100 blue rectangle. What I could find by Googling doesn't seem to help me, as those questions either apply to 8bit surfaces (and setting palettes — my bpp is 32 here) or are left unanswered.</p> <p>So, I would like to know how should I properly blit a generated surface onto a SDL screen.</p> <p><strong>Edit:</strong> I see it was an error in the parameter ordering. The line in question should read</p> <pre><code>SDL_BlitSurface(layer, NULL, screen, NULL); </code></pre> <p>Still, I am having trouble to achieve the same effect in my more complex C++ program. I will post the relevant parts of the code here:</p> <p>main.cpp:</p> <pre><code>int main(int argc, char** argv) { SDLScreen screen(1024, 700, "Hello, SDL!"); SDL_Event event; SDLMenu menu; bool shouldQuit = false; menu.setBounds(200, 100, 200, 600); menu.setFontName("NK211.otf"); menu.setFontSize(36); menu.setEffect(sdlteShadowText); menu.addItem("New game"); menu.addItem("Load game"); menu.addItem("Save game"); menu.addItem("Exit"); menu.render(); while (!shouldQuit) { menu.draw(screen.getSurface()); SDL_Flip(screen.getSurface()); SDL_Delay(10); while (SDL_PollEvent(&amp;event)) { if (event.type == SDL_QUIT) { shouldQuit = true; } else if (event.type == SDL_KEYUP) { if (event.key.keysym.sym == SDLK_q) { shouldQuit = true; } } } } } </code></pre> <p>SDLMenu.cpp:</p> <pre><code>void SDLMenu::setSelectionColorRGB(int r, int g, int b) { SDL_VideoInfo* info = (SDL_VideoInfo*)SDL_GetVideoInfo(); selectionColor = SDL_MapRGB(info-&gt;vfmt, r, g, b); } void SDLMenu::render() { SDLText* current = NULL; SDL_VideoInfo* info = (SDL_VideoInfo*)SDL_GetVideoInfo(); if (!items-&gt;empty()) { current = getItemAt(currentItem); selectionRect = getItemRect(current); setSelectionColorRGB(0,0,255); selectionCanvas = SDL_CreateRGBSurface(SDL_HWSURFACE, selectionRect-&gt;w, selectionRect-&gt;h, info-&gt;vfmt-&gt;BitsPerPixel, info-&gt;vfmt-&gt;Rmask, info-&gt;vfmt-&gt;Gmask, info-&gt;vfmt-&gt;Bmask, info-&gt;vfmt-&gt;Amask); SDL_FillRect(selectionCanvas, selectionRect, selectionColor); SDL_SaveBMP(selectionCanvas, "selection.bmp"); // debug } for (list&lt;SDLText*&gt;::iterator i = items-&gt;begin(); i != items-&gt;end(); i++) { (*i)-&gt;render(); } } void SDLMenu::draw(SDL_Surface* canvas) { int currentY = bounds.y; if (selectionCanvas != NULL) { SDL_BlitSurface(selectionCanvas, NULL, canvas, selectionRect); } for (list&lt;SDLText*&gt;::iterator i = items-&gt;begin(); i != items-&gt;end(); i++) { (*i)-&gt;draw(bounds.x, currentY, canvas); currentY += fontSize + itemGap; } } </code></pre> <p>SDLScreen.cpp:</p> <pre><code>SDLScreen::SDLScreen(int w, int h, string t, int d) : width(w), height(h), depth(d), title(t) { SDL_Init(SDL_INIT_EVERYTHING); SDL_WM_SetCaption(title.c_str(), NULL); refresh(); } void SDLScreen::refresh() { screen = SDL_SetVideoMode(width, height, 32, SDL_HWSURFACE); } </code></pre> <p>The selection rectangle for the active menu item should be blue, but it shows up in black. The file <code>selection.bmp</code> is also all black.</p> <p><strong>Edit 2:</strong> I found out what created the problem. The <code>selectionRect</code> was set relative to the screen, while the <code>selectionCanvas</code> had the width and height of a particular menu item. So, the filling was done out of bounds of the <code>selectionCanvas</code>. Adding separate <code>SDL_Rect</code> for filling solved the problem.</p> <pre><code>SDL_Rect fillRect; fillRect.x = 0; fillRect.y = 0; fillRect.w = selectionRect-&gt;w; fillRect.h = selectionRect-&gt;h; SDL_FillRect(selectionCanvas, &amp;fillRect, selectionColor); // and later... SDL_BlitSurface(selectionCanvas, NULL, canvas, selectionRect); </code></pre>
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