Some Issues Implementing the Debug Renderer

[cuppajoeman]

Hi there,

I'm working on a game in opengl3.3 and I've been trying to implement the debug renderer so that I can see what jolt sees with respect to my game.

So far I've built up a project where a player can move around a basic world aim move and jump using Jolt, right now all the rendering is being done manually, and just so happens to line up with what jolt sees for collisions etc...

8mb.video-zU7-pJCHRf50.mp4

I'm pretty new to c++ and I tried my best to grasp how DebugRendererImp.cpp/hpp works, and to implement that with respect to opengl, the result I got so far was this (note that the debug drawing is done in wireframe mode in grey)

8mb.video-s60-U76RQMlH.mp4

What I did was as follows:

• Instead of BatchImpl I created TriangleData, instead of being a render primitive it simply holds the triangle's data for later use. Note that I had to create the class ThatIHaveToMake to mirror the structure in the BatchImpl or else I couldn't get it to work.
• I implemented the function DrawGeometry in my class, which given some geometry attempts to render the triangles with opengl.

The result, as seen in my previous video is a bunch of crazy triangles, which seem to be changing all the time.

I would be very grateful if anyone could take a look over my code in physics_debug_renderer.cpp to provide any hints on how I can debug this, or if there are any glaring issues.

---

Notes:

• The representation of the world's MeshShape is correct, I know this to be true because when moving around the world collisions occur correctly, therefore the data being stored by Jolt with respect to the map's MeshShape is correct.
• I have verified that the code in DrawGeometry can correctly render triangle data, for example by instead using a single triangle it correctly renders that in space, this means that the issue is with the data being stored in the triangleBatches or how I'm parsing it so I'm quite certain the issue is within my CreateTriangleBatch method.
• The debug renderer is able to render the wireframe of the stone walls on the sides perfectly, but all the other things seem very garbled, so at least one TriangleData gets created correctly by the CreateTriangleBatch function.
• No calls to DrawLine were being made so I know the issue is in DrawGeometry
• No calls to CreateTriangleBatch where the arguments are vertices along with indices occur, so I believe the issue is in CreateTriangleBatch(const Triangle *inTriangles, int inTriangleCount)
• My game doesn't use a LOD system yet, I don't fully understand how I'm supposed to use the LOD array.
• Sometimes when I try to load a triangle batch I get back a null or 0x20 pointer, which I don't fully understand
• I find it very strange that the triangle data seems to be changing (causing the flickering effect), I have no idea how/why that could happen

[jrouwe]

I think the biggest problem is that you're storing a pointer to the triangle data that you get passed in:

https://github.com/opengl-toolbox/mwe_physics_world_with_character/blob/c25f6898390d7b48daef7b87b87c6722442a21c8/graphics/physics_debug_renderer/physics_debug_renderer.hpp#L63-L68

however that data is destructed the moment CreateTriangleBatch returns. You need to create a copy.

[cuppajoeman]

That was right on, when I copy the data instead of using the pointer, it works well:

8mb.video-8Eg-y4zd2gNx.mp4

[MrOnlineCoder]

My game doesn't use a LOD system yet, I don't fully understand how I'm supposed to use the LOD array.
I don't know the correct way there, but I used just the first LOD passed to DrawGeomtetry and it worked fine for my purposes of just being able to visually verify the shapes/bodies are matching my world geometry:

auto lod = inGeometry.GetPtr()->mLODs[0];

[cuppajoeman]

@jrouwe I changed my code to instead just use the first LOD value and it seems to work fine, can you explain why this happens and we don't have to iterate through the LOD array?

[jrouwe]

The LOD array is only needed in case you can't render the scene at the target FPS anymore (i.e. if it consists of hundreds of thousands of triangles), if you don't have that then picking the first LOD is fine.

You should know where your camera is and you get the bounding box as part of the DrawGeometry function so you can calculate the distance from camera to the box and pick the lowest LOD whose distance is smaller than the calculated distance. The lod scale also factors into this (this is for when an object has been scaled) the complete formula is here:

JoltPhysics/TestFramework/Renderer/DebugRendererImp.cpp

Line 339 in 94124f0

if (dist_sq <= src_instance.mLODScaleSq * Square(geometry_lods[lod].mDistance))

[cuppajoeman]

Ok, that makes sense, if the renderer starts lagging, I'm going to look more into this

[cuppajoeman]

Hey @jrouwe I was just going back and making sure my project compiles correctly, when I compile my source code (which contains an implementation of the DebugRenderer. Here's the header file and the source) using either Release or Debug everything compiles and works properly.

If I don't specify the build type I get the following linker error:

[ 96%] Linking CXX executable mwe_physics_world_with_character
/usr/bin/ld: CMakeFiles/mwe_physics_world_with_character.dir/main.cpp.o: in function `PhysicsDebugRenderer::~PhysicsDebugRenderer()':
main.cpp:(.text._ZN20PhysicsDebugRendererD2Ev[_ZN20PhysicsDebugRendererD5Ev]+0x22): undefined reference to `JPH::DebugRenderer::~DebugRenderer()'
/usr/bin/ld: CMakeFiles/mwe_physics_world_with_character.dir/graphics/physics_debug_renderer/physics_debug_renderer.cpp.o: in function `PhysicsDebugRenderer::PhysicsDebugRenderer()':
physics_debug_renderer.cpp:(.text+0x15): undefined reference to `JPH::DebugRenderer::DebugRenderer()'
/usr/bin/ld: physics_debug_renderer.cpp:(.text+0xa6): undefined reference to `JPH::DebugRenderer::Initialize()'
/usr/bin/ld: physics_debug_renderer.cpp:(.text+0xb7): undefined reference to `JPH::DebugRenderer::~DebugRenderer()'
/usr/bin/ld: CMakeFiles/mwe_physics_world_with_character.dir/graphics/physics_debug_renderer/physics_debug_renderer.cpp.o:(.data.rel.ro._ZTI20PhysicsDebugRenderer[_ZTI20PhysicsDebugRenderer]+0x10): undefined reference to `typeinfo for JPH::DebugRenderer'
/usr/bin/ld: CMakeFiles/mwe_physics_world_with_character.dir/graphics/graphics.cpp.o: in function `JPH::PhysicsSystem::DrawBodies(JPH::BodyManager::DrawSettings const&, JPH::DebugRenderer*, JPH::BodyDrawFilter const*)':
graphics.cpp:(.text._ZN3JPH13PhysicsSystem10DrawBodiesERKNS_11BodyManager12DrawSettingsEPNS_13DebugRendererEPKNS_14BodyDrawFilterE[_ZN3JPH13PhysicsSystem10DrawBodiesERKNS_11BodyManager12DrawSettingsEPNS_13DebugRendererEPKNS_14BodyDrawFilterE]+0x44): undefined reference to `JPH::BodyManager::Draw(JPH::BodyManager::DrawSettings const&, JPH::PhysicsSettings const&, JPH::DebugRenderer*, JPH::BodyDrawFilter const*)'
collect2: error: ld returned 1 exit status
make[3]: *** [CMakeFiles/mwe_physics_world_with_character.dir/build.make:265: mwe_physics_world_with_character] Error 1
make[2]: *** [CMakeFiles/Makefile2:222: CMakeFiles/mwe_physics_world_with_character.dir/all] Error 2
make[1]: *** [CMakeFiles/Makefile2:229: CMakeFiles/mwe_physics_world_with_character.dir/rule] Error 2
make: *** [Makefile:169: mwe_physics_world_with_character] Error 2

I tried figuring out how to fix this, and I found that in your implementation you have this line:

JoltPhysics/TestFramework/Renderer/DebugRendererImp.cpp

Line 16 in 5c9d3b0

#include <Jolt/Renderer/DebugRenderer.cpp>

where you include the source file rather than the header file under some specific conditions. When I include that source file (DebugRenderer.cpp) it reduces the number of errors:

[ 95%] Linking CXX executable mwe_physics_world_with_character
/usr/bin/ld: CMakeFiles/mwe_physics_world_with_character.dir/graphics/graphics.cpp.o: in function `JPH::PhysicsSystem::DrawBodies(JPH::BodyManager::DrawSettings const&, JPH::DebugRenderer*, JPH::BodyDrawFilter const*)':
graphics.cpp:(.text._ZN3JPH13PhysicsSystem10DrawBodiesERKNS_11BodyManager12DrawSettingsEPNS_13DebugRendererEPKNS_14BodyDrawFilterE[_ZN3JPH13PhysicsSystem10DrawBodiesERKNS_11BodyManager12DrawSettingsEPNS_13DebugRendererEPKNS_14BodyDrawFilterE]+0x44): undefined reference to `JPH::BodyManager::Draw(JPH::BodyManager::DrawSettings const&, JPH::PhysicsSettings const&, JPH::DebugRenderer*, JPH::BodyDrawFilter const*)'
collect2: error: ld returned 1 exit status
make[3]: *** [CMakeFiles/mwe_physics_world_with_character.dir/build.make:265: mwe_physics_world_with_character] Error 1
make[2]: *** [CMakeFiles/Makefile2:222: CMakeFiles/mwe_physics_world_with_character.dir/all] Error 2
make[1]: *** [CMakeFiles/Makefile2:229: CMakeFiles/mwe_physics_world_with_character.dir/rule] Error 2
make: *** [Makefile:169: mwe_physics_world_with_character] Error 2

But I don't believe this is a good workaround. Do you have any idea what's going on here when I don't specify the built type?

[jrouwe]

The manual inclusion of DebugRenderer.cpp in DebugRendererImp.cpp is there to be able to use the debug renderer without JPH_DEBUG_RENDERER being defined inside the Jolt library and is probably not something you should try to replicate. The Samples app uses it because it has no other way of rendering stuff.

Your link error probably indicates that Jolt has been built without the JPH_DEBUG_RENDERER define and that your own code has it defined. Make sure this matches on both sides.

[cuppajoeman]

I was building jolt without specifying a build type, and that was the problem, I found out through the docs that you have to build using Debug or Release to have it work.