All `Texture`s loaded from `.bmp` files render only monochrome+transparent, with RGBA colors flipped (on `RectangleShape`s)

[metaleap]

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Describe your issue here

First described in this forum-thread post: any Texture::loadFromFile-loaded .bmp Textures render colorless (when bound to a RectangleShape — my only scenario here).

It isn't just that bitmap file: I have tried others present in my system (hardly any of course... only ones found were from golang.org/x/image/testdata). It just happens with all of them, and multiple image-viewers on my system all display all of them in the correct RGB coloring.

The issue is quite-possibly this. Doing a repo-wide code search, there's no sight of any GL_BGR in the SFML master branch (and plenty for GL_RGB naturally). Has anyone ever used a (non-B/W) .bmp file successfully? =) It is a rarely-used legacy format after all.

Your Environment

• OS / distro / window manager: VoidLinux x86_64, i3wm
• SFML version: 2.6.1 (system-wide distro-provided package)
• Compiler / toolchain: g++ 12.2.0
• Special compiler / CMake flags: --debug -std=c++20 -march=native -O0

Steps to reproduce

sf::RectangleShape myRect;
myRect.setSize({512, 256});
myRect.setOrigin(0, 0);
myRect.setPosition(0, 0);
myRect.setFillColor(sf::Color::Green);

sf::Texture myTex;
myTex.loadFromFile("/home/myname/some/local/bitmap.bmp");
myRect.setTexture(&myTex);
const auto size_tex = myTex.getSize();
myRect.setTextureRect(sf::IntRect {0, 0, (int)(size_tex.x), (int)(size_tex.y)});

window.draw(myRect);

Expected behavior

Textured rectangle shows the image in its original RGB colors, as all sorts of locally-installed image viewers do. Example:

Actual behavior

Textured rectangle shows the image as transparent-monochrome: the rectangle's background fill color (green) is the backdrop and actual pixels show as black. Like so:

[ChrisThrasher]

We have unit tests that load a BMP image and test a few pixel values, one of which is a non-greyscale pixel. That much is working. That seems to reinforce your theory that the problem lies not in image loading but rather with how images are drawn to the screen.

@binary1248 What do you think of this?

[metaleap]

We have unit tests that load a BMP image and test a few pixel values, one of which is a non-greyscale pixel. That much is working.

Good to know, yes indeed that makes the GL_BGR hypothesis most likely I guess.

Btw. I guess it isn't really monochromely rendering, just showed that way to me with the .bmps I did have, plus the Green rect bgcolor. Now with Cyan instead, I can tell that whites show as Cyan (ie. full alpha), blues and greens are preserved, and yellows show as stark over-green, likely blending the Cyan in. (I'll best go with a White rect bgcolor to really analyze the generated .bmps here =)

[kimci86]

This is expected because of this: myRect.setFillColor(sf::Color::Green);

See setFillColor documentation

This color is modulated (multiplied) with the shape's texture if any.

[metaleap]

True that must be it actually! Since I'm getting correct blues greens and yellows (aka reds) here, it's all just due to the multiplication. Thanks much @kimci86 and @ChrisThrasher . I do remember reading that part of the docs earlier, but it clearly didn't resurface in the here-and-now..