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Rebasedlinuxhostgl - #224
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Headless contexts in the compatibility profile through EGL, with no surface at all (EGL_KHR_surfaceless_context): every drawable is already a framebuffer object. The display is Mesa's surfaceless platform where there is one, else the first EGL device, else the default. libEGL is opened at run time; the entry points the crate calls by name come from libGL (glvnd). A swap reads back with glReadPixels: there is no CPU-addressable surface yet. Looking entry points up by name needs a table. glvnd and Mesa answer any gl* name with a callable stub, so a missing function never comes back null, and Exec::func relies on null to fall back from an SGI or EXT name to the core one. avail.rs, generated from the pinned registry by tools/gl_avail.py, says which version or extension provides each name; the backend looks a name up only when the context has it. On Linux arm64 C's char is unsigned, so the shader entry points take c_char, not i8. Tested on Debian 12 arm64 in Parallels (virgl, OpenGL 4.0 compatibility, Mesa 22.3.6): the crate's 27 tests pass, and in an IP28 IRIX 6.5.22 guest glcheck passes with the reference checksum. Co-Authored-By: Claude Opus 5.5 <[email protected]>
The names the crate uses for itself started at 0x7F000000 and counted up. Apple's GL hands a program the lowest free name, so that was safe there; Mesa hands out one above the highest in use, so after a name of ours it gave the program the next one we were about to take, and the two were bound to different targets. gltest's SGIS_texture_filter4, SGIS_sharpen_texture and SGIS_detail_texture checks failed on Linux with GL_INVALID_OPERATION (glBindTexture target mismatch). Counting down from u32::MAX leaves Mesa no "one above", and it goes back to the lowest free name. gltest now passes 167/167 for n32 and o32 on Linux; nothing changes on the Mac. Co-Authored-By: Claude Opus 5.5 <[email protected]>
FEATURES.md, iris-gui-README.md, iris-gui's build-info line and TODO.md said host GL was macOS only. CHANGELOG: the EGL backend, what building and running it need, and how it was tested. rules/hostgl/linux-egl-and-mesa.md: the stub-for-every-name problem and avail.rs, Mesa's texture names, c_char, and what is linked versus opened. The registry README names gl_avail.py. Co-Authored-By: Claude Opus 5.5 <[email protected]>
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