The Old New Thing

Code - The Old New Thing

What is the process by which the cursor gets set?

November 21, 2006 Nov 21, 2006 11/21/06
Raymond Chen
Commenter LittleHelper asked, "Why is the cursor associated with the class and not the window?" This question makes the implicit assumption that the cursor is associated with the class. While there is a cursor associated with each window class, it is the window that decides what cursor to use. The cursor-setting process is described in the ...

It takes only one program to foul an upgrade

November 20, 2006 Nov 20, 2006 11/20/06
Raymond Chen
"Worst software ever." That was Aaron Zupancic's cousin's reaction to the fact that Windows XP was incompatible with one program originally designed for Windows 98. Then again, commenter Aargh! says "The bad code should be fixed, period. If it can't be fixed, it breaks, too bad." Perhaps Aargh! can send a message to Aaron's ...

Using DIB sections to perform bulk color mapping

November 16, 2006 Nov 16, 2006 11/16/06
Raymond Chen
When doing dithering, one operation you have to do for every pixel is map it (more accurately, map a modified version of it) to the nearest color in your available palette. Since this is part of the dithering inner loop, you need this operation to be as fast as possible.¹ A common technique for this is to precompute the nearest palette ...

Manipulating the DIB color table for fun and profit

November 15, 2006 Nov 15, 2006 11/15/06
Raymond Chen
If you create a DIB section at 8bpp or lower, then it will come with a color table. Pixels in the bitmap are represented not by their red/blue/green component values, but are instead indices into the color table. For example, a 4bpp DIB section can have up to sixteen colors in its color table. Although displays that use 8bpp or lower are ...

Blitting between color and monochrome DCs

November 14, 2006 Nov 14, 2006 11/14/06
Raymond Chen
When blitting between color and monochrome DCs, The text foreground and background colors play a role. We saw earlier that when blitting from a monochrome DC to a color DC, the color black in the source turns into the destination's text color, and the color white in the source turns into the destination's background color. This came in handy...

What do bitwise operations mean for colors?

November 13, 2006 Nov 13, 2006 11/13/06
Raymond Chen
Someday, you're going to pass a raster operation to the function that entails bit manipulation. Something like perhaps, or possibly the dreaded . These bitwise operations make perfect sense for monochrome bitmaps, since those are one bit per pixel anyway. But what does it mean for color bitmaps? What do you get when you "and" together forest...

Converting an HRESULT to a Win32 error code: Diagram and answer to exercise

November 10, 2006 Nov 10, 2006 11/10/06
Raymond Chen
Here's the diagram from How do I convert an HRESULT to a Win32 error code?. If you are offended by VML, cover your ears and hum for a while. The little sliver at the top is the mapping of zero to zero. The big white box at the bottom is the mapping of all negative numbers to corresponding negative numbers. And the rainbow represents the...

How do I convert an HRESULT to a Win32 error code?

November 3, 2006 Nov 3, 2006 11/3/06
Raymond Chen
Everybody knows that you can use the macro to convert a Win32 error code to an , but how do you do the reverse? Let's look at the definition of : If the value is less than or equal to zero, then the macro returns the value unchanged. Otherwise, it takes the lower sixteen bits and combines them with and . How do you reverse this ...