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The DirectDraw modes are entirely replaced by the Direct3D mode. We strongly recommend to use the Direct3D mode instead of the DirectDraw modes. |
In this mode, the image data is written to the non-visible area of the VGA card. The requirements for this are the DirectDraw driver, sufficient memory on the VGA card and back buffer support from the VGA cards’ manufacturer. If a back buffer is not available on the VGA card, it will automatically be stored on the PC. Exactly the same goes for overlay data. Under ideal circumstances there would be image memory as well as overlay memory in the back buffer of the VGA card. Then the VGA chip does a bit block transfer of both memory areas to the visible area of the VGA board during the VSYNC period. The result is a live image display with overlaid text and graphics. The image refresh frequency and the load on the CPU are dependent upon the color depth setting and upon the location of the back buffer (i.e. either the main memory of the PC or the image memory of the VGA card.).
Mode = IS_SET_DM_DIRECTDRAW
Fig. 37: DirectDraw back buffer mode
