Top 10 GLScene Tips for Faster 3D Development

Optimizing Performance in GLScene ProjectsGLScene is a powerful, component-based 3D graphics library for Delphi and C++Builder that simplifies creating and managing scenes, objects, and rendering pipelines. As projects grow in complexity—more objects, higher-resolution textures, dynamic lighting, and real-time interaction—performance becomes critical. This article walks through practical, tested strategies to optimize GLScene applications so they run smoothly across a range of hardware.

1. Profile first, guess later

Before changing code, measure. Use a profiler or simple timing instruments to find where the app spends time: scene traversal, state changes, GPU-bound rendering, texture uploads, or physics/logic. Common profiling methods:

Built-in Delphi/C++Builder profilers or sampling tools.
Insert timestamps (QueryPerformanceCounter) around suspect sections.
Use GLScene’s FPS monitor (TGLCadencer, TGLSceneViewer’s statistics) to track frame time and bottlenecks.

Focus optimization efforts on the slowest 20% of code that causes 80% of the delay.

2. Reduce draw calls and state changes

Each GL draw call and OpenGL state change (bind texture, enable/disable features) has overhead. Minimize them by:

Batching geometry with similar materials into single meshes.
Using shared materials and textures across objects to avoid repeated binds.
Grouping objects by shader and render state, rendering them in contiguous blocks.
Avoiding frequent glEnable/glDisable calls; set states once per frame where possible.

In GLScene: combine submeshes with TMeshObject or use TGLProxyObject/TGLActor to organize grouped rendering.

3. Use level-of-detail (LOD)

Decrease geometric complexity for distant objects:

Implement LOD using TGLLOD or manually swap mesh detail levels based on camera distance.
Create simplified meshes (decimated versions or impostors) for mid- and far-range.
Use billboards or sprites for far-away vegetation and background objects.

LOD reduces vertex processing and fragment work significantly on complex scenes.

4. Optimize geometry and vertex data

Efficient vertex data saves CPU and GPU time:

Use indexed triangle lists to eliminate duplicate vertices.
Keep vertex attributes compact — use floats only when needed; don’t store unused normals/texcoords.
Interleave vertex attributes for better memory locality.
Precompute tangents/binormals if using normal mapping to avoid per-frame recalculation.
Use Vertex Buffer Objects (VBOs) / Vertex Array Objects (VAOs) to store geometry on the GPU. GLScene supports VBOs—enable them for static geometry.

Static meshes: upload once to GPU. Dynamic meshes: minimize updates, update only changed portions.

5. Reduce fragment workload

Pixel shading often dominates. Strategies:

Lower texture resolutions where acceptable. Use mipmaps (GL_NEAREST_MIPMAP_LINEAR / GL_LINEAR_MIPMAP_LINEAR) to reduce sampling cost for smaller screen areas.
Use compressed texture formats (S3TC/DXT) to reduce memory bandwidth.
Avoid large overdraw: sort opaque geometry front-to-back to leverage early-z rejection; render transparent objects last.
Simplify fragment shaders—remove expensive operations and conditionals where possible.
Limit the number of lights affecting each pixel (deferred shading can help for many dynamic lights).

6. Manage textures wisely

Textures can be memory and bandwidth hogs:

Use texture atlases to reduce binds for many small textures (sprites, UI elements).
Generate mipmaps when creating textures to improve cache efficiency and visual quality at distance.
Stream textures: load/resolution-switch textures based on proximity or memory pressure.
Unload unused textures and free GPU memory during level transitions.

GLScene offers helpers for texture management—leverage TGLMaterialLibrary and shared textures.

7. Efficient scene graph usage

A scene graph simplifies management but can hide inefficiencies:

Keep the graph shallow and avoid excessive nesting with many small nodes; each node traversal has cost.
Disable or detach nodes that are not visible or needed (Object->Visible := False).
Use bounding volumes and spatial partitioning (octrees, quadtrees) to cull large unseen portions. GLScene provides TGLDirectOpenGL and optional culling helpers; integrate your own spatial structure for large worlds.
Avoid per-frame recalculation of transforms when objects are static.

8. Occlusion culling and frustum culling

Frustum culling: ensure you cull objects outside the camera frustum before sending geometry to GPU. GLScene provides frustum checks—enable and tune them.

Occlusion culling: more advanced. Use hardware queries (GL_ARB_occlusion_query) or software approaches to skip rendering objects blocked by nearer geometry. Only implement when it clearly reduces fragment cost compared to query overhead.

9. Use efficient lighting strategies

Lighting can be expensive:

Prefer baked/static lighting for non-dynamic elements (lightmaps).
For dynamic scenes, use clustered or tiled forward rendering or deferred shading to decouple lighting cost from object count.
Limit per-object light counts. Use light volumes or influence radii.
Use cheaper lighting models where possible (Phong vs. physically based for distant or low-priority objects).

10. Optimize transparency and blending

Transparency often causes overdraw and prevents some early-z optimizations:

Reduce transparent pixel count by limiting areas that need blending; use alpha testing for cutouts.
Sort and batch transparent objects to minimize state changes.
Consider screen-space alternatives (post-process cutouts) for certain effects.

11. Multithreading and background tasks

While OpenGL context access is typically single-threaded, many tasks can be parallelized:

Do asset loading, mesh generation, and texture decompression in background threads.
Use worker threads for physics, AI, and non-render math.
Prepare data for the GPU on background threads, then upload in a single main-thread operation.
Use command buffering or job systems to minimize main-thread stall.

Be careful with thread synchronization and OpenGL context usage—use shared contexts or transfer resources on the main thread.

12. Reduce CPU-GPU synchronization

Excessive sync stalls (glFinish, glGet* queries) harm performance:

Avoid glFinish and minimize glReadPixels or blocking queries.
Use asynchronous queries and fences (ARB_sync) when you need GPU progress info.
Double-buffer dynamic buffers to avoid waiting for GPU to finish using a buffer before updating it.

13. Optimize shaders

Shaders run for every vertex/fragment; optimize them:

Use branching sparingly; prefer precomputed pathways if branches are divergent.
Use precision qualifiers where supported.
Reuse common computations and move invariant calculations to vertex shader or precompute on CPU.
Profile shader performance (GPU vendor tools) and focus on hotspots.

14. Memory and resource limits

Monitor and limit memory usage:

Keep an eye on VRAM usage; excessive swapping to system memory kills performance.
Reuse buffers and textures where possible instead of reallocating.
For large worlds, implement streaming of meshes and textures.

15. Platform-specific tweaks

Different GPUs/drivers behave differently:

Test on target hardware and adjust texture compression, shader versions, and buffer usage accordingly.
For mobile/low-power devices, prefer simpler shaders, smaller textures, and lower polycounts.
Use vendor tools (NVIDIA Nsight, AMD Radeon GPU Profiler) for deep analysis.

16. Practical checklist and examples

Quick checklist:

Profile to find hotspots.
Batch geometry and reduce state changes.
Enable VBOs/VAOs for static geometry.
Implement LOD and culling.
Compress and mipmap textures; use atlases.
Minimize fragment shader complexity and overdraw.
Move work off the main thread where safe.

Example: converting many small dynamic meshes into a single VBO and using a texture atlas reduced draw calls from 3,000 to ~120 in a medium scene, increasing FPS from 20 to 75 on mid-range hardware.

17. Tools and resources

GLScene components and documentation for VBOs, LOD, material libraries.
GPU vendor profilers for shader & driver-level insights.
Texture compression tools (PVRTexTool, Compressonator).
Mesh decimation and LOD generation tools.

Conclusion

Effective optimization balances CPU and GPU work, reduces wasted work (overdraw, unnecessary state changes), and targets the real bottlenecks identified by profiling. Apply these strategies iteratively: measure, change one thing, and measure again. With careful batching, culling, LOD, texture management, and judicious use of modern GPU features, GLScene projects can achieve smooth, scalable performance across devices.