FMSLogo Code

Use modff (on float) instead of modf (on double) for computing alpha values to improve performance.
Double prevision was unnecessary since the number was converted to 0-4096, which only has 12 bits of precision.

Cleanup: inline "HDC paintDeviceContext" local variable.
It was initialized far from the location where it was used and it was only used once.

Remove some redundant computation in turtlepaste when interpolating colors.
There's no need to combine the RGB color components into a single int only to separate them into the RGB components later.

Update turtlepaste to use a single wxImage for editing the portion of the screen that it updates.
This eliminates a copy (improves both memory and speed)

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.