问题
Problem
Windows Mobile / Directdraw: Rotate video stream
The video preview is working, all I need now is a way to rotate the image. I think the only way to handle this is to write a custom filter based on CTransformFilter that will rotate the camera image for you. If you can help me to solve this problem, e.g. by helping me to develop this filter with my limited DirectDraw knowledge, the bounty is yours.
Background / Previous question
I'm currently developing an application for a mobile device (HTC HD2, Windows Mobile 6). One of things the program needs to do is to take pictures using the built-in camera. Previously I did this with the CameraCaptureDialog offered by the Windows Mobile 6 SDK, but our customer wants a more user-friendly solution.
The idea is to preview the camera's video stream in a control and take a high resolution picture (>= 2 megapixels) using the camera's photo function, when the control is clicked. We did some research on the topic and found out the best way to accomplish this seems to be using Direct Draw.
The downsides are that I never really used any native windows API and that my C++ is rather bad. In addition to this I read somewhere that the Direct Draw support of HTC phones is particularity bad and you will have to use undocumented native HTC libraries calls to take high quality pictures.
The good news is that a company offered us to develop a control that meets the specifications stated above. They estimated it would take them about 10 days, which lead to the discussion if we could develop this control ourself within a reasonable amount of time.
It's now my job to research which alternative is better. Needless to say it's far too less time to study the whole architecture and develop a demo, which lead me to the following questions:
Questions no longer relevant!
- Does any of you have experience with similar projects? What are your recommendations?
- Is there a good Direct Draw source code example that deals with video preview and image capturing?
回答1:
Well if you look at the EZRGB24 sample you get the basics of a simple video transform filter.
There are 2 things you need to do to the sample to get it to do what you want.
1) You need to copy x,y to y,x.
2) You need to tell the media sample that the sample is now Height x Width instead of Width x Height.
Bear in mind that the final image will have exactly the same number of pixels.
To solve 1 is relatively simple. You can calculate the position of a pixel by doing "x + (y * Width)". So you step through each x and y calculate the position that way and then write it to "y + (x * Height)". This will transpose the image. Of course without step2 this will look completely wrong.
To solve 2 you need to get the AM_MEDIA_TYPE of the input sample. You then need to find out what the formatType is (Probably FormatType_VideoInfo or FormatType_VideoInfo2). You can thus cast the pbFormat member of AM_MEDIA_TYPE to either a VIDEOINFOHEADER or a VIDEOINFOHEADER2 (Depending on the FormatType). You need to now set VIDEOINFOHEADER[2]::bmiHeader.biWidth and biHeight to the biHeight and biWidth (respectively) of the input media sample. Everything else should be the same as the input AM_MEDIA_TYPE.
I hope that helps a bit.
回答2:
This question will help you get some details about DirectDraw. I did some research about this some time ago and the best I could find was this blog post (also mentioned in the above question). The post presents an extension of the CameraCapture sample in the SDK.
However, don't have high expectations. It seems that the preview and the picture taken will only work in small resolution. Although DirectDraw does describe a way of configuring the resolution, there is no guarantee that this will be properly implemented by the driver.
So from my experience what you have read is true. The only way to do it will be to use HTC drivers. So, if you don't want to spend endless days in reverse engineering for a doubtful result, let someone else do the job for you. If you want to give it a shot, try xda-developers forum.
来源：https://stackoverflow.com/questions/2289637/directdraw-rotate-video-stream