Mastodawn

Just learned that there is no way for a GLSL shader to send data to the CPU side program. I think, at least. No way to emit debugging information at all, not even a puts.

At least if I understand, "Uniforms are so named because they do not change from one shader invocation to the next within a particular rendering call thus their value is uniform among all invocations."

Thought I could define a uniform, then set that to some debugging value in the shader.

@kertinker You should be able to write into SSBOs.

@landelare Oh... sorry, I can't use storage buffer objects. GLEW_ARB_shader_storage_buffer_object is 0.

@kertinker @landelare image load store is another option
https://wikis.khronos.org/opengl/Image_Load_Store
https://registry.khronos.org/OpenGL/extensions/ARB/ARB_shader_image_load_store.txt

@aeva @landelare Looks interesting! Hm...
printf("%d\n", GLEW_ARB_shader_image_load_store);
0
Looks like not that one either. GL_OES_mapbuffer maybe...? I might be hosed.

@kertinker @aeva You don't printf into these. Use imageStore() if you want to use ARB_shader_image_load_store.

@landelare @aeva I was using printf in a CPU side program, to print the "GLEW_ARB_shader_image_load_store" variable, which I think the OpenGL Extension Wrangler would set to 1, if ARB_shader_image_load_store was supported by my graphics card.

I made sure to call glewInit and have a valid context and all.

@landelare as of version 1.1.0, GLEW signals extension availability with variables containing boolean values, so while the examples KT is posting look like name constants, they're mutable binary values that the initialization code sets up. relevant docs: https://glew.sourceforge.net/basic.html

@kertinker what GL version are you targeting and what platform? for a sanity check, could you post what GLEW_ARB_vertex_program is after init?

GLEW: The OpenGL Extension Wrangler Library

@kertinker @landelare also if you happen to be on linux could you paste the output of glxinfo to a pastebin somewhere and link it here?

@aeva @landelare Oh, sure. I don't have a "glxinfo" command, but visualinfo produces this: https://nopaste.net/l92XzrU5kr which... oddly includes GL_EXT_shader_image_load_store.

I'm clearly doing something wrong. Not sure how I could get a working OpenGL program running, without it saying extensions that are supported, are supported. Maybe you have to set a specific... mode, before they get supported?

@kertinker @landelare if you can, post your GL initialization code

@aeva @landelare https://nopaste.net/aTFTXWDVRU

Other than that just the usual gtk init and creating a GtkGlArea.

@kertinker @landelare what is the GL major and minor version reported by your program?

@kertinker @landelare I'm not familiar with GtkGlArea, but I spotted this in the docs https://docs.gtk.org/gtk4/method.GLArea.set_required_version.html

You have to call gtk_gl_area_set_required_version before the widget's rendering context is created, but I imagine if you set it to 4.6 (based on your earlier visualinfo paste) then you should be able to see the extensions you are missing. Ideally you'll want to set it to the lowest required version you need, but 4.6 is fine for debugging.

Gtk.GLArea.set_required_version

@kertinker @landelare it occurred to me just now if there's an explicit GL context initialization step needed that is missing entirely, then GLEW might be reporting 0 for most or all extensions depending on the platform you're on

@aeva @kertinker This crap is why I'm using DirectX.

@landelare Can't blame OpenGL in this case. @aeva pointed out I missed an initialization function, in GTK not OpenGL, so it would have failed even if I used DirectX. Looks like the problem is me not reading the documentation correctly.

@kertinker @landelare these things happen, but we got it working :D

@aeva @landelare Now my cludgey pointless geometry shader draws a box *three* times!

@kertinker @landelare woohoo! :D