Large images with Direct2D

Question

Currently I am developing application for the Windows Store which does real time-image processing using Direct2D. It must support various sizes of images. The first problem I have faced is how to handle the situations when the image is larger than the maximum supported texture size. After some research and documentation reading I found the VirtualSurfaceImageSource as a solution. The idea was to load the image as IWICBitmap then to create render target with CreateWICBitmapRenderTarget (which as far as I know is not hardware accelerated). After some drawing operations I wanted to display the result to the screen by invalidating the corresponding region in the VirtualSurfaceImage source or when the NeedUpdate callback fires. I supposed that it is possible to do it by creating ID2D1Bitmap (hardware accelerated) and to call CopyFromRenderTarget with the render target created with CreateWICBitmapRenderTarget and the invalidated region as bounds, but the method returns D2DERR_WRONG_RESOURCE_DOMAIN as a result. Another reason for using IWICBitmap is one of the algorithms involved in the application which must have access to update the pixels of the image.

The question is why this logic doesn't work? Is this the right way to achieve my goal using Direct2D? Also as far as the render target created with CreateWICBitmapRenderTarget is not hardware accelerated if I want to do my image processing on the GPU with images larger than the maximum allowed texture size which is the best solution?

Thank you in advance.

Answer 1

You are correct that images larger than the texture limit must be handled in software.

However, the question to ask is whether or not you need that entire image every time you render.

You can use the hardware accel to render a portion of the large image that is loaded in a software target.

For example,

• Use ID2D1RenderTarget::CreateSharedBitmap to make a bitmap that can be used by different resources.
• Then create a ID2D1BitmapRenderTarget and render the large bitmap into that. (making sure to do BeginDraw, Clear, DrawBitmap, EndDraw). Both the bitmap and the render target can be cached for use by successive calls.
• Then copy from that render target into a regular ID2D1Bitmap with the portion that will fit into the texture memory using the ID2D1Bitmap::CopyFromRenderTarget method.
• Finally draw that to the real render target, pRT->DrawBitmap