Implement GLSL rendering for M420 and NV12

[Nir-Az]

Summary

• Implement working GLSL fragment shader for M420 format (was previously throwing "cannot be rendered with GLSL yet")
• Add new NV12 GLSL renderer with full pipeline: shader, C/C++ API, dual processing block with CPU fallback
• Add M420 and NV12 rendering cases to the viewer upload path
• Remove M420 and NV12 from the "rendering not supported" list

Test plan

• Verified NV12 GLSL rendering with platform camera — image displays correctly
• Verified M420 GLSL rendering — image displays correctly
• Confirmed GLSL shader is active by injecting deliberate color change
• Verified CPU fallback works when GLSL for rendering is unchecked
• Build passes on Windows (Debug)

M420 on D585S

NV12 on platform camera

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR adds GPU (GLSL) color conversion/rendering support for the M420 and NV12 formats in the RealSense GL pipeline, and wires the new capability through the public GL processing API and the viewer upload path.

Changes:

• Implement GLSL fragment shader-based conversion for M420 and introduce a new NV12 GLSL converter with CPU fallback via dual_processing_block.
• Expose an NV12 GL decoder in the C/C++ GL processing APIs and export it from the GL shared library.
• Update the viewer/rendering upload path to handle M420 and NV12, and remove them from the “rendering not supported” list.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/gl/rs-gl.cpp	Adds rs2_gl_create_nv12_decoder and wires it into the GL processing-block factory with CPU fallback.
src/gl/realsense-gl.def	Exports the new NV12 GL decoder symbol on Windows.
src/gl/nv12-to-rgb-gl.h	Declares the new librealsense::gl::nv12_to_rgb GPU processing block.
src/gl/nv12-to-rgb-gl.cpp	Implements the NV12 GLSL shader and processing block (texture upload + FBO render to RGB).
src/gl/m420-to-rgb-gl.cpp	Replaces the prior “not supported” runtime error with a working GLSL shader path for M420.
src/gl/CMakeLists.txt	Adds the new NV12 GL converter sources to the GL library build.
include/librealsense2-gl/rs_processing_gl.hpp	Introduces rs2::gl::nv12_decoder C++ wrapper class.
include/librealsense2-gl/rs_processing_gl.h	Adds the C API declaration for rs2_gl_create_nv12_decoder.
common/viewer.cpp	Stops flagging M420/NV12 as “rendering not supported” in the viewer UI.
common/subdevice-model.cpp	Switches NV12 conversion to use the new GL decoder wrapper.
common/rendering.h	Adds M420 and NV12 handling to the texture upload/render path (using the processing blocks).

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[remibettan]

WD