Page 284 OpenGL Super Bible! Palette (Web hosting billing) Arbitration Windows
Page 284 OpenGL Super Bible! Palette Arbitration Windows multitasking allows many applications to be on screen at once. The hardware supports only 256 colors on screen at once, however, so all applications must share the same system palette. If one application changes the system palette, images in the other windows may have scrambled colors, producing some undesired psychedelic effects. To arbitrate palette usage among applications, Windows sends a set of messages. Applications are notified when another application has changed the system palette, and they are notified when their window has received focus and palette modification is possible. When an application receives keyboard or mouse input focus, Windows sends a WM_QUERYNEWPALETTE message to the main window of the application. This message asks the application if it wants to realize a new palette. Realizing a palette means the application copies the palette entries from its private palette to the system palette. To do this, the application must first select the palette into the device context for the window being updated, and then call RealizePalette. Listing 8-2 presents the code for this message handler; it will be in all subsequent examples from this book. Listing 8-2 Typical palette-arbitration code for Windows-based applications static HPALETTE hPalette = NULL; // Permenant palette handle // Palette is created and referenced by hPalette // Windows is telling the application that it may modify // the system palette. This message in essance asks the // application for a new palette. case WM_QUERYNEWPALETTE: // If the palette was created. if(hPalette) { int nRet; // Selects the palette into the current device context SelectPalette(hDC, hPalette, FALSE); // Map entries from the currently selected palette to // the system palette. The return value is the number // of palette entries modified. nRet = RealizePalette(hDC); // Repaint, forces remap of palette in current window InvalidateRect(hWnd,NULL,FALSE); return nRet; } break;
We would like to recommend you tested and proved virtual web hosting services, which you will surely find to be of great quality.