FMSLogo Code

Improve the performance of turtlepaste by writing all pixels to the screen at once, instead of pixel-by-pixel.
This was done to reclaim some lost performance caused by setting the scroller and zoom within the PaintDeviceContext, so that FMSLogo 8.3.0 won't be perceived to be slower than FMSLogo 8.2.0.

On my Windows 10 machine, this makes the sprite benchmark take 1/3rd the time.
On my Windows XP machine, this makes no difference.

Add a missing "const" to prevent accidental modification of a buffer

Move some code around to avoid costly calls to modf().
This improved performance of the sprite benchmark by 10%.

Ignore gcov metadata files (created when fmslogo.exe is built with COVERAGE=1)

Improve the performance of turtlepaste by getting all pixels from the screen at once, instead of pixel-by-pixel.
This was done to reclaim some lost performance caused by setting the scroller and zoom within the PaintDeviceContext, so that FMSLogo 8.3.0 won't be perceived to be slower than FMSLogo 8.2.0.

Change the background for BITMAPTURTLE.SMOKETEST to reach into the corners.

Cache a value instead of recomputing it.
This is less for performance than to make it clear that it's the same value being reused.

Replace "HDC TempMemDC" with a wxMemoryDC for better portability.

Avoid multiple calls to GetScreenHorizontalScrollPosition/GetScreenVerticalScrollPosition
gprof says that this takes a long time, but I don't know if that's trustworthy.
Even if not, calling those methods half as many times isn't bad.

Don't use a back buffer was used when drawing regular turtles.
This was a regression that was accidently introduced when adding a back buffer for all bitmapped turtles (instead of just sprites).
This regression caused a 200% slowdown in the squiral benchmark.

It doesn't make sense to use a back buffer when drawing normal turtles, as there is other logic to draw them directly to the screen as the turtle is moved, bypassing any back buffer.