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Support negative height in BMP files #18

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Merged
merged 3 commits into from
Aug 6, 2019
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cogliano
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@cogliano cogliano commented Aug 1, 2019

The BMP file format standard allows for the bitmap height to be defined as a negative number. When negative, it means that instead of the origin being at the lower left it is instead at the upper left. This file change supports those images where the origin is in the upper left.

Reference: https://en.wikipedia.org/wiki/BMP_file_format

The BMP file format standard allows for the bitmap height to be defined as a negative number. When negative, it means that instead of the origin being at the lower left it is instead at the upper left when the height is negative. This file change supports those images where the origin is in the upper left.
@ladyada
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ladyada commented Aug 1, 2019

do you have an example to test with

@cogliano
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cogliano commented Aug 1, 2019

I have a test file with a negative height if you need to test this.

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cogliano commented Aug 1, 2019

Here is the file (it is an autostereogram so the apparent random bits are intentional :-)

https://www.dropbox.com/s/dcpiorjwkiwgj22/asgadafruit.bmp?dl=0

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matt-land commented Aug 1, 2019

I can test this later with the supplied file tonight or tomorrow.

@cogliano Do you think you can make the changes to pass the build? It looks like its a pylint error.

If not, I can PR against yours to make the change.

theight = height
if theight < 0:
theight = 0 - theight
bitmap = bitmap(width, theight, colors)
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Can you just declare the bitmap as below, and remove lines 65-67?

bitmap = bitmap(width, abs(height), colors)

This would save the (very limited) memory and time spent allocating the object "theight", since it isn't used again.

Edit: I got the line numbers wrong the first time. I tested the PR with and without this change, and both worked.

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Thanks, I should have seen that. I just made a pull request.

@matt-land matt-land merged commit 5caff1f into adafruit:master Aug 6, 2019
adafruit-adabot added a commit to adafruit/Adafruit_CircuitPython_Bundle that referenced this pull request Sep 17, 2019
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3 participants