The Old New Thing

History - The Old New Thing

Why are RECTs endpoint-exclusive?

February 18, 2004 Feb 18, 2004 02/18/04
Raymond Chen
Endpoint-exclusive RECTs and lines are much easier to work with. For example, the width of a rectangle is , and its height is . If rectangles were endpoint-inclusive, then there would be annoying +1's everywhere. End-point exclusive rectangles also scale properly. For example, suppose you have two rectangles (0,0)-(100,100) and (100,100)-(...

The arms race between programs and users

February 16, 2004 Feb 16, 2004 02/16/04
Raymond Chen
There is a constant struggle between people who write programs and the people who actually use them. For example, you often see questions like, "How do I make my program so the user can't kill it?" Now, imagine if there were a way to do this. Ask yourself, "What would the world be like if this were possible?" Well, then there would be some ...

Bad version number checks

February 13, 2004 Feb 13, 2004 02/13/04
Raymond Chen
Version numbers. Very important. And so many people check them wrong. This is why Windows 95's GetVersion function returned 3.95 instead of 4.0. A lot of code checked the version number like this: Now consider what happens when the version number is reported as 4.0. The major version check passes, but the minor version check fails since 0...

Sure, we do that

February 11, 2004 Feb 11, 2004 02/11/04
Raymond Chen
The DirectX video driver interface for Windows 95 had a method that each driver exposed called something like "DoesDriverSupport(REFGUID guidCapability)" where we handed it a capability GUID and it said whether or not that feature was supported. There were various capability GUIDs defined, things like GUID_CanStretchAlpha to ask the ...

Adjustor thunks

February 6, 2004 Feb 6, 2004 02/6/04
Raymond Chen
Yesterday we learned about the layout of COM objects and I hinted at "adjustor thunks". If you find yourself debugging in disassembly, you'll sometimes find strange little functions called "adjustor thunks". Let's take another look at the object we laid out last time: In the diagram, p is the pointer returned when the IPersist interface...

The layout of a COM object

February 5, 2004 Feb 5, 2004 02/5/04
Raymond Chen
The Win32 COM calling convention specifies the layout of the virtual method table (vtable) of an object. If a language/compiler wants to support COM, it must lay out its object in the specified manner so other components can use it. It is no coincidence that the Win32 COM object layout matches closely the C++ object layout. Even though COM ...

The white flash

January 23, 2004 Jan 23, 2004 01/23/04
Raymond Chen
If you had a program that didn't process messages for a while, but it needed to be painted for whatever reason (say, somebody uncovered it), Windows would eventually lose patience with you and paint your window white. Or at least, that's what people would claim. Actually, Windows is painting your window with your class background brush. Since...

The history of calling conventions, part 5: amd64

January 14, 2004 Jan 14, 2004 01/14/04
Raymond Chen
The last architecture I'm going to cover in this series is the AMD64 architecture (also known as x86-64). The AMD64 takes the traditional x86 and expands the registers to 64 bits, naming them rax, rbx, etc. It also adds eight more general purpose registers, named simply R8 through R15. Here's a sample: On entry to CallThatFunction, the ...