Upgrade MuJoCo Renderer to OpenGL 3

[ShravanTata]

• Fully support the basic.cc example with both fixed-function and modern OpenGL 3 pipelines.
• Introduce clear separation between legacy and modern renderer code (render_x vs render3_x).
• Provide a runtime or compile-time toggle for selecting the rendering backend.

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Tasks & Progress

1. Code Organization

• Keep legacy rendering path in render/render_x.
• Introduce modern pipeline in render/render3_x.

2. Shader-based Renderer (render3_x)

• Minimal GLSL shader setup (vertex + fragment).
• VAO/VBO for drawing geometry in basic.cc.
• MVP matrix handling for camera (replace glPushMatrix/glPopMatrix).
• Ensure legacy GL still compiles & runs when shaders are disabled.

3. Legacy Renderer (render.h)

• Keep existing fixed-function pipeline intact.
• Verify basic.cc still runs without changes when using legacy path.

4. Mesh & Geometry

• Add VBO/VAO support in the new renderer.
• Map MuJoCo mesh data to modern buffer objects.
• Keep legacy glBegin/glEnd path for now.

5. Example Migration

• Update basic.cc to select renderer via toggle/flag.
• Ensure visual parity between legacy and GL3 paths.

6. Transforms

• Replace glPushMatrix/glPopMatrix in GL3 path with uniform matrices.
• Keep existing matrix stack in legacy path for now.

7. Lighting & Materials

• Reimplement fixed-function lighting in GLSL for GL3 path.
• Match visual output with legacy path.

8. Textures

• Modern texture allocation (glTexStorage2D / glTexSubImage2D) in GL3 path.
• Preserve legacy glTexImage2D pipeline.

9. Framebuffers

• Migrate offscreen rendering to FBOs in GL3 path.
• Keep legacy buffer bindings as fallback.

10. Misc

• Update copyright to 2025

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[bd-gpasternak]

you might be interested in these changes too #2888 would help debug things with nsight.

[ShravanTata]

you might be interested in these changes too #2888 would help debug things with nsight.

Thanks for the pointer and commits @bd-gpasternak. I will keep track of those changes.