Advanced MFC Programming

Chapter 10. Bitmap
image can have only 2 colors, and will be automatically converted to mono chrome fomat no matter what
kind of data we use to initialize the bitmap.
Draw original
image at (1, 1)
Combine them
using bit-wise OR
operation
Draw inverted
image at (0, 0)
Resulted outline
Figure 10-5. Generate the outline that should be drawn with highlighted color
Raster Operation Mode
Another issue needs to be discussed here is how to draw the outline portion using specified color
without affecting rest part of the image. In order to implement this, we can treat the two outline bitmaps as
masks, and draw only the unmasked pixels with specified colors. This procedure is similar to that of
drawing bitmaps with transparency.
When calling function CDC::BitBlt(…) or CDC::StretchBlt(…) to paint the bitmap, we always need
to specify the drawing mode, which specifies how to combine the pixels in the source bitmap with the
corresponding destination pixels. This drawing mode is also called raster operation mode, because it is
applicable only to raster devices (Contary to the raster devices are vector devices, for example, a plotter is a
vector device). We have many choices such as bit-wise AND, OR, XOR etc. Actually, we can specify more
complex combinations among the following three different objects when calling the above two functions:
the pixel in the source bitmap, the corresponding pixel in the target device, and the brush currently being
selected by the DC. We can specify up to three Boolean bit-wise operations among them.
For example, the following operation will draw the outline on the destination bitmap with the brush
color:
(Brush Color) XOR (Destinaton Color) AND (Source Color) XOR (Brush Color)
The reason is simple: After the first operation (between the brush and destination pixels), the pixels in
the target device will become the XOR combination between the original pixel colors and the brush color.
Next, this XORed result will be ANDed with the source bitmap (Only the outlined part is black, rest part is
white), the outlined part on the target device will become black and the rest part remains unchanged (still
XORed result from the first operation). Then we do XOR again between the target device and the brush, for
the outlined part, this operation will fill it with the brush color (A ^ 0 = A); for the rest part, this will
resume the original color for every pixel (A ^ B ^ A = B).
Chiselled Effect
With the following steps, we can create chiselled effect:
1) Create a brush with shadowed or highlighted color.
1) Paint the destination with the brush using bit-wise XOR operation mode.
1) Draw the mask bitmap on the target device using bit-wise AND operation mode.
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