Image Manager > Image Manager API > ActiveX Controls > Display Control

Common Vision Blox supports DirectDraw.

When using DirectDraw the image data is written to offscreen VGA memory, any overlay data is then applied and the image is subsequently copied to the onscreen VGA memory, all of these steps can be handled by the VGA hardware.

It is very easy to imagine there could be substantial differences in the drawing speed depending on the graphics hardware being used, a particularly important factor in choosing the VGA card is the size of video RAM.

If there is not enough RAM available for both onscreen AND offscreen memory then DirectDraw driver will emulate the hardware functions, if this occurs then the use of DirectDraw may slow the display process down compared with non-DirectDraw display which has been highly optimised in Common Vision Blox.

Another benefit of using the display technique described above is that the overlay is applied to the image data a the refresh rate of the video and not the image data, this creates a flicker free overlay.

If DirectDraw is unable to allocate enough memory and emulates hardware functions the overlay is still flicker free.

Common Vision Blox only supports DirectDraw in 16-bit (64K colors) and 32-bit True Color VGA modes.

No other VGA color depths are supported.

It is important to understand how much the function and speed of DirectDraw depend on the VGA card that is being used as well as the drivers supplied by the VGA card vendor.

The AGP based G400 and G450 VGA cards from Matrox and the AGP-based ATI VGA cards have proved to be fast and reliable devices.

If you wish to disable DirectDraw in the system then please refer to the DirectDrawEnabled property of the Display Control for further details.

•It is recommended to use a high quality VGA card

•It is important to ensure that your VGA card has at least three times the memory required for a single display, a minimum of 16MB is recommended

•It is recommended to always use the drivers supplied by the VGA card vendor and not those shipped with Windows, the performance and quality of the DirectDraw drivers are as important as the DirectDraw libraries

•DirectDraw is ONLY support at 16-Bit and 32-Bit colour depths

•Enabling DirectDraw does not guarantee DirectDraw will be used, it only guarantees that Common Vision Blox will attempt to use it, the above criteria also have to be met

DirectDraw

DirectDraw

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