I’m really scratching my head on this one, and I hope someone can help me out. I’ve been working on a project using OpenGL where I’ve set up an instanced indexed mesh that uses vertex, geometry, and fragment shaders to render correctly. Everything was smooth sailing until I decided to introduce tesselation to my pipeline with Tesselation Control Shaders (TCS) and Tesselation Evaluation Shaders (TES).
The thing is, once I hooked up the TCS and TES, my mesh vanished from the screen! It’s like I turned the lights off or something. At first, I thought it was a simple issue, so I diligently checked several key things. I changed my drawing call to `glDrawElementsInstanced(GL_PATCHES, indexCount, GL_UNSIGNED_INT, (GLvoid *)0, instances);`, and also set up the patch size with `glPatchParameteri(GL_PATCH_VERTICES, GLint(this->patchSize));`, ensuring it doesn’t exceed `GL_MAX_PATCH_VERTICES`, which is 128 on my setup. I even went through the shader compilation and linking processes, and everything seemed to be fine.
But here’s where it gets bizarre. I was initially using OpenGL 4.1, and everything was compiling well but still nothing rendered. So I decided to upgrade to OpenGL 4.5, thinking maybe it would fix the issue. That’s when I started getting a linking error that says “TEInstanceID not declared as an output from the previous stage.”
Here’s the kicker—I can still see the geometry when I skip the GS altogether and just use the tessellation shaders. But I want the TCS and GS to work together. I went for a passthrough on the tessellation shaders, but it feels like something’s just not playing nice between the stages.
Can anyone help me pinpoint what might be going wrong? I’ll drop all my shader code here for context. Maybe you can spot something I couldn’t! What am I missing? Any insights would be greatly appreciated!
It sounds like you’re running into a tricky issue with shader stages! When you’re dealing with both tessellation shaders and geometry shaders, there are a few things to check since they interact in specific ways.
First, make sure that your TCS is properly outputting the necessary data that the GS requires. If your GS expects certain attributes but they’re not being passed from the TCS, you’ll run into issues like the output error you’re seeing. Double-check your shader code to confirm that you are declaring the outputs of the TCS correctly.
Your TCS should have outputs defined like this:
layout (vertices = 3) out; // or whatever your patch size is out vec3 tessCoord; // Example outputAnd then in your GS, make sure you’re using those outputs:
in vec3 tessCoord[]; // matching the output from TCSIf you’re getting “TEInstanceID not declared as an output”, it typically means that either you didn’t declare that variable in your TCS output or you are not appropriately passing it to the rest of the shader pipeline. Make sure to follow the naming conventions and that the variable is accessible.
Also, since you’re trying to use the GS, ensure the inputs for the GS match what your previous shader stage outputs. Mismatched types or missing variables can prevent proper linking.
As for the rendering issue, when switching between OpenGL versions, keep an eye on any added requirements or deprecated features that might affect your shaders. It’s possible that something may have changed between 4.1 and 4.5 that you’re not accounting for.
Lastly, if it helps, try debugging step by step by isolating each shader stage and confirm they work individually first before combining them. This may help narrow down where things are going wrong.
Good luck sorting this out, and don’t hesitate to share your shader code if you want others to help spot any specific issues!
The linking error you’re encountering (“TEInstanceID not declared as an output from the previous stage”) points to a mismatch in interface variables between the Tessellation Evaluation Shader (TES) and the Geometry Shader (GS). Unlike vertex-to-fragment or vertex-to-tessellation stages, each shader interface variable must explicitly match by name, type, and qualifier. Specifically, when a GS is active following tessellation shaders, the output variables of your TES must exactly match (by type, qualifier, and name) the input variables declared in the GS. It’s common to overlook explicitly declaring built-in variables correctly at each stage; for example, “gl_InstanceID” is built-in and accessible, but “TEInstanceID” is not recognized unless explicitly defined in TES’s outputs.
To ensure your pipeline works correctly with TCS, TES, and GS together, explicitly declare any custom interface variables used by the GS as outputs in the TES. For instance, define something like
out int TEInstanceID;in your TES and correspondinglyin int TEInstanceID[];(as an array) in your GS input interface. Alternatively, rely on built-in variables when possible, such asgl_InvocationIDorgl_PrimitiveID, which don’t need explicit passing. Additionally, double-check your tessellation shaders—if you use pass-through implementations, ensure that they explicitly forward vertex outputs to interface variables also defined in subsequent shaders. Confirm that the GS input layout qualifier matches the TES output primitive type: for tessellated meshes, typically you’d uselayout(triangles)or similar in GS input declaration.