Pixels seem to have inconsistent widths on emulated screen about b-em HOT 7 CLOSED

Interesting. On the Allegro4 version the code that blits the bitmap from the BBC onto the screen in vidalleg.c is rather different between Windows and Linux. The Windows code implements window re-sizing, scaling the output as appropriate, but the Linux code does not. The Linux code is also missing the PAL simulation. I did look to see if they could be made more similar but allocating a video bitmap on Linux crashes. AFAIK this is an Allegro bug or a bug in the particular backend Allegro4 uses.

On the Allegro 5 port there is now one set of video blit code with the same options on both platforms. It chooses an initial window size to get 1:1 and you can re-size it from there.

One test of your theory would be to save a screenshot from B-Em's own menu rather than via the desktop and compare.

from b-em.

See 1cb9b46

Checking the in-line function upscale_only at vidalleg.c line 161 it was upscaling - by two pixels.

from b-em.

Thanks for this. I've had a go with a simple test program to draw a sawtooth wave:

10MODE 0
20X%=0
30Y%=0
40IY%=4
50FOR I%=1 TO 1000
60PLOT 69,X%,Y%
70X%=X%+2
80Y%=Y%+IY%
90IF Y%=1020 OR Y%=0 THEN IY%=IY%*-1
100NEXT

I've attached screenshots of this from my Linux desktop:.

and from b-em's own screenshot feature (converted from BMP to PNG format using the 'convert' command line tool to keep github happy):

b-em's own screenshot has much more regular pixels, although it seems to omit the bottom-most row of pixels (the image is 640x510 and the rightmost bottom point of the sawtooth has its tip missing)

I'll see if I can do an Allegro 5 build later and try that.

from b-em.

Looks like 1cb9b46e368933eb6e850a49e3f0af1f2dd59b61has fixed this for Allegro4, thanks!

from b-em.

The bottom row of pixels is still missing on the b-em-generated screenshots, FWIW; shall I raise a separate issue for that?

from b-em.

Try the latest commit which should fix the failure to save the last line in a screenshot.

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Works a treat, thanks!

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