Drawing Images - Win32 Programmer's Reference

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Drawing Images

To draw an image, you use the ImageList_Draw or ImageList_DrawEx function. You specify the handle of an image list, the index of the image to draw, the handle of the destination device context, a location within the device context, and one or more drawing styles.

When you specify the ILD_TRANSPARENT style, ImageList_Draw or ImageList_DrawEx uses a two-step process to draw a masked image. First, it performs a logical AND operation on the bits of the image and the bits of the mask. Then it performs a logical XOR operation on the results of the first operation and the background bits of the destination device context. This process creates transparent areas in the resulting image; that is, each white bit in the mask causes the corresponding bit in the resulting image to be transparent.

Before drawing a masked image on a solid color background, you should use the ImageList_SetBkColor function to set the background color of the image list to the same color as the destination. Setting the color eliminates the need to create transparent areas in the image and enables ImageList_Draw or ImageList_DrawEx to simply copy the image to the destination device context, resulting in a significant increase in performance. To draw the image, specify the ILD_NORMAL style in a call to ImageList_Draw or ImageList_DrawEx.

You can set the background color for a masked image list at any time so that it draws correctly on any solid background. Setting the background color to CLR_NONE causes images to be drawn transparently by default. To retrieve the background color of an image list, use the ImageList_GetBkColor function.

The ILD_BLEND25 and ILD_BLEND50 styles dither the image with the system highlight color. These styles are useful if you use a masked image to represent an object that the user can select. For example, you can use the ILD_BLEND50 style to draw the image when the user selects it.

A nonmasked image is copied to the destination device context using the SRCCOPY raster operation. The colors in the image appear the same regardless of the background color of the device context. The drawing styles specified in ImageList_Draw or ImageList_DrawEx also have no effect on the appearance of a nonmasked image.

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