BMP TASImage artefacts and crashes

[ferdymercury]

Describe the bug

This script produces the following result:

#include "TCanvas.h"
#include "TASImage.h"

void test_asimage()
{
    new TCanvas("bmp","bmp");
    auto bmp = new TASImage("./screenshot.bmp");
    bmp->Draw();

    new TCanvas("png","png");
    auto png = new TASImage("./screenshot.png");
    png->Draw();
}

Expected behavior

Both PNG and BMP pictures should be the same. the left picture looks like it has some byte misalignment.

To Reproduce

1. Download the screenshot files screenshots.zip
2. Run the code snippet above

Setup

ROOT 6.22/02 on Ubuntu18

[ferdymercury]

A potential reason might be that it is not handling the negative height correctly. See https://docs.microsoft.com/en-us/previous-versions//dd183376(v=vs.85)?redirectedfrom=MSDN

biHeight
The height of the bitmap, in pixels.
If biHeight is positive, the bitmap is a bottom-up DIB and its origin is the lower-left corner.
If biHeight is negative, the bitmap is a top-down DIB and its origin is the upper-left corner.

See https://github.com/root-project/root/blob/master/graf2d/asimage/src/libAfterImage/bmp.c#L199

[couet]

I see the issue too on my Mac. Not sure how to fix it. I will investigate what you suggest here.

[ferdymercury]

Thanks. One side comment. There is a problem in the way libAfterImage is built. Even if I build ROOT in 'debug mode', libAfterImage is built with -O3 optimization flag. I think the build mode should be propagated also to libAfterImage.

Otherwise it's much more difficult to debug this issue.

[ferdymercury]

See:

2004-09-21  sasha

	* added mandatory -O3 in libAfterImage and libAfterBase improving
	  performance significantly;

I think it would be better if this only happened in 'Release Mode'. In debug mode, other flags like -g should be passed instead.

https://github.com/root-project/root/blob/master/graf2d/asimage/src/libAfterImage/configure#L3244
https://github.com/root-project/root/blob/master/graf2d/asimage/src/libAfterImage/configure.in#L210

[ferdymercury]

I confirm that with a positive height BMP, the result is rendered correctly by ROOT:

https://www.fileformat.info/format/bmp/sample/7ce642a25ca34f2087f2e8ec0f97713c/download

[couet]

I confirm that with a positive height BMP, the result is rendered correctly by ROOT

Do you have a fix ?

[ferdymercury]

Nope, unfortunately the BMPs are generated by a Pulse Generator, and they are always with negative height :S

[ferdymercury]

I think it might not be related at all to the negative height, but to the file format.

Can you check if the attached BMP file crashes for you also? It was generated with GIMP.

screenshot.bmp.zip