{"id":221,"date":"2009-11-19T08:51:14","date_gmt":"2009-11-19T13:51:14","guid":{"rendered":"http:\/\/www.e-consystems.com\/blog\/?p=221"},"modified":"2023-08-15T12:34:55","modified_gmt":"2023-08-15T07:04:55","slug":"creating-an-effective-image-viewer-in-windows-ce","status":"publish","type":"post","link":"https:\/\/www.e-consystems.com\/blog\/system-on-module-som\/creating-an-effective-image-viewer-in-windows-ce\/","title":{"rendered":"Creating an effective image viewer in Windows CE"},"content":{"rendered":"

There are some cases where we may need to develop a DLL or application to show the images on the devices. For example, an Image viewer will be needed to show the picture after taking a snap shot from the camera using a direct show camera application. Windows Mobile supports the image viewer for this purpose, However if you are developing a custom camera application <\/em><\/strong> in Windows CE\/Windows Mobile, you have to show the captured image with a custom developed image viewer. There you may need additional image manipulation functionality like zooming, rotation and cropping etc. Unfortunately Windows CE 6.0 doesn\u2019t have an image viewer application at all. But Windows CE supports Imaging APIs to handle the various file types like JPG, BMP, TIFF and GIF etc\u2026<\/span><\/p>\n

Effective way of handing the JPEG images on Image viewer<\/strong><\/span><\/p>\n

Imaging APIs are accessed through COM interfaces. To Load the image you have to use IImagingFactory<\/span> <\/em>Interface with the class ID CLSID_ImagingFactory<\/span>.<\/em> Following code snippet show the procedure to load the imaging COM interfaces.<\/span><\/p>\n

CoCreateInstance (CLSID_ImagingFactory, NULL,CLSCTX_INPROC_SERVER, IID_IImagingFactory, (void **)&m_pImgFactory).<\/span><\/em> <\/span><\/strong>The m_pImgFactory is the pointer to the IImagingFactory. <\/span><\/em><\/span><\/p>\n

Opening an image file<\/strong><\/span><\/p>\n

Use the IImagingFactory ::CreateImageFromFile(const WCHAR* filename, IImage** image) <\/span><\/em>to open the file.<\/span><\/p>\n

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Simple way to draw the Image on the Screen<\/strong><\/span><\/p>\n

We can use the <\/em>IImage :: Draw( HDC <\/em>hdc, const RECT* <\/em>dstRect,OPTIONAL const RECT* <\/em>srcRect)<\/em><\/span> <\/span><\/strong>to draw the image on the screen with the required dstRect <\/em>size. But when our application Menu area may over write some part of the image, we may need to redraw the image in WM_PAINT on our window proc. IImage::Draw() <\/em>function will decode the image and draw every time, while calling the function. This makes your application slow, while clicking the Menu.<\/span><\/p>\n

To avoid this, we can use the <\/strong>Image::SetImageFlags(ImageFlagsCaching) <\/span><\/em>to cache the bitmap area and to reuse it for the next time. The disadvantage is, <\/em>IImage::Draw()<\/span><\/em> may fail because of\u00a0 insufficient memory to cache the higher Mega Pixel files. This will happen in Windows Mobile (virtual memory limitations for each process). So we need to find the alternate solution, that should be effectively handling the memory and to maintain the performance.
\n<\/strong><\/span><\/p>\n

Effective way to draw the image on the screen<\/strong><\/span><\/p>\n

The Effective way is, creating the bitmap for the exact required screen size once and uses it for several times. Following are the steps to create and draw the bitmap.<\/span><\/p>\n