The drawPoint() method takes the x and y coordinates of the point to be drawn. These are specified relative to the upper-left corner of the image, which is point (0,0).
The y coordinate is used as an index into the array of xbmRow objects. The high-order bits of the x coordinate are used to compute an index into the array of JavaScript numbers representing the row. The low-order bits are then used to calculate the bit offset for the desired pixel coordinate, which is turned on.
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