Seeking help for lighting issues

[fenggy]

I am currently developing an editor and everything is going smoothly. However, I have encountered usage issues with lighting and would like to receive assistance. The specific description is as follows:

I want to implement a basic material function similar to MeshBasicMaterial in Threejs, which allows objects that are not affected by lighting to have their color or texture set regardless of lighting. I have already used a custom shader to implement this function, but there are still texture requirements in the future. Therefore, I want to use the system's built-in PhongGL to achieve it. However, not only how I set the color and light position, but I still cannot get the custom effect. Can you give me some ideas?

The following is my custom Sharder effect that is not affected by lighting and displays the object's own color.

This is the system's built-in rendering and key code. As the scene rotates, the color changes too much.

Hope to give some ideas, thank you.

[mosra]

Hi!

This looks like in case of the builtin Phong you have the light positioned relative to the camera (and so when rotating the faces that are directly facing the camera look brightest), while with your custom shader you have the light positioned statically in the scene and so the lighting doesn't change when rotating.

To convert a light position that's static in the scene to a camera-relative position, transform it with the camera matrix. I.e., something like setLightPositions({camera.cameraMatrix().transformPoint(lightPosition), 1.0f}).

[fenggy]

Finally solved, I am very happy and excited. This problem has been bothering me for a long time, but I can only have the energy to solve it after completing the drag and drop function.
At present, I have not set the lighting position. With your reminder, I seem to have solved it using another method. Please refer to the following:
Related lighting configurations

`

m_phongShader = Shaders::PhongGL{
	Shaders::PhongGL::Configuration{}
		.setFlags(Shaders::PhongGL::Flag::ObjectId)
	.setLightCount(1)
};
m_phongShader.setLightPosition(0, { 1.0f, 1.0f, 1.0f,0.0f });
m_phongShader.setLightColor(0, { 1.0f,1.0f,1.0f });

Color configuration.

const auto ambientColor = _color * 0.7f;
const auto diffuseColor = _color * 0.3f;

_shader1.setTransformationMatrix(transformationMatrix)
	.setNormalMatrix(transformationMatrix.normalMatrix())
	.setProjectionMatrix(camera.projectionMatrix())
	.setAmbientColor(ambientColor)
	.setDiffuseColor(diffuseColor)
	.setSpecularColor(Color4{ 0.0f })
	.setShininess(10.0f)

`

I can finally use the full functionality of Shaders:: PhongGL. My shader function is too weak, and PhongGL function is both complex and powerful. I originally wanted to port it for use, but at my current level, I find it an impossible task to complete.
Thank you for providing the powerful Magnum. The more I use it, the more comfortable it becomes. Next, I will prepare to use imgui and start building the IDE environment.
By the way, can I use the latest imgui library since my Magnum is the version from April 2025?
Thank you again. @mosra

[mosra]

By the way, can I use the latest imgui library since my Magnum is the version from April 2025?

Yes, it should work with any ImGui version from the past ~2 years.

[fenggy]

This is a clever solution, the color will still change with rotation, it's just not obvious, but it still solves the current problem. Let's do this for now, and we will try adjusting the position of the light source later.

[mosra]

I don't understand what you mean, sorry. What happens, exactly?

Just in case it wasn't clear initially -- you need to update the light position every frame, because the cameraMatrix() will be different every frame. From the code above it looks like you're doing it just once (accessing the _camera-> member rather than camera. passed to draw().

[fenggy]

My editor is designed for digital twin applications, but I hope that objects in the scene are not affected by lighting. I followed the approach of other software and first used a custom shader to make one side of the cube appear darker, which not only has a 3D effect but also avoids lighting issues. However, custom shaders can only set colors, and I will need to add mapping functionality in the future, so I still want to use built-in shaders to implement it.
I don't know if it's a problem with my requirements themselves or if the implementation method is incorrect, but the results are not ideal. Now I am using a flexible solution to set a certain ratio between setAmbientColor and setDiffuseColor. Although the colors of each side will change during rotation, the transition is more natural and barely acceptable.
As you said, it has been tested. Although the code only has one line, it is actually called in both camera rotation and onPaint. As long as the position is updated in real-time, the rendering effect will become a flat 3D like effect, but the specific reason has not been found yet.
I have also looked for some examples of using Magnum, but have not found any relevant methods to draw on.
I don't know if I described it clearly?
The following is the relevant code and screenshots.

[mosra]

Apologies for the delay, end of the year is always busy... I'm still not sure what exactly you mean, so I'll try to ask clarifying questions:

Your problem is still what you said originally, i.e. that you want the lighting to not change when camera is moved, right? So, you want it like in the first GIF, and not like in the second, right?

What's the hierarchy of the scene you have? Is camera a root object? If it isn't, making it a root object will make it easier to reason about when it comes to light positions and such. Similarly, make sure the scene the camera is looking at is not parented to the camera itself (or sharing common parents), that also makes things unnecessarily confusing.

The last image looks flat likely due to two things:

1. The ambient color is too strong and thus it hides any actual diffuse lighting that varies based on vertex normals. Try reducing that to less than 0.8.
2. If that alone doesn't help and the scene is uniformly flat, then it's because the light is basically behind the camera all the time, even if you rotate. Which might be due to the scene hierarchy being complicated as I said above. Try simplifying it so the camera and objects in the scene are not related to each other in any way.

Hope I understood what you mean :)

[fenggy]

Sorry, it seems that I am more suited to coding. Written expression is my weakness, especially when it comes to 3D, which I am just getting into and still in the exploratory stage.

Yes, the effect I want is the first GIF. The lighting is fixed and does not change with the camera.

The demo is a modification made on the magnum-bootstrap-base-wxwidgets example, featuring a simple scene and camera settings, and should be the root node.

Thank you for your reply. Currently, I am using ImGUI to integrate and design an IDE. Once the GUI is functioning properly, I will try to address this issue. It's possible that it's related to the camera position.

Additionally, it must be mentioned that Platform::Application (sdl) + ImGuiIntegration::Context is really cool and convenient.

Thanks

[mosra]

No problem -- feel free to just ZIP up the whole code you have and upload it here (or send it to mosra@centrum.cz if you don't want to share it publicly). I'll run it on my end and try to figure out what's wrong, that'll be faster than trying to describe ithe same with words :)