SIGSEGV when calling glGenBuffers
lazarus / 70-OpenGL

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LemonParty · 2024-12-18 18:29

Hello.
I trying to use glGenBuffers function from unit GLext this way:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i var  VBO:
GLuint;{...}glGenBuffers(1, @VBO);And I getting SIGSEGV on
glGenBuffers(1, @VBO); line. What I missing?

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zamtmn · 2024-12-18 18:47

If you use GLext.pp? you need run
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
Load_GL_version_1_5or later GL version init function, and it need
return true

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Thaddy · 2024-12-18 19:15

Quote from: LemonParty on December 18, 2024, 07:29:11 pmHello.
I trying to use glGenBuffers function from unit GLext this way:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i var  VBO:
GLuint;{...}glGenBuffers(1, @VBO);And I getting SIGSEGV on
glGenBuffers(1, @VBO); line. What I missing?
Memory allocation... Basic mistake.
VBO needs memory... Allocmem, Getmem, New...

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zamtmn · 2024-12-18 19:28

Thaddy
The first principle is to read the documentation. And you often don't
do that in a hurry to answer the question

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H₂SO₄ · 2024-12-19 06:26

Quote from: Thaddy on December 18, 2024, 08:15:45 pmMemory
allocation... Basic mistake.
VBO needs memory... Allocmem, Getmem, New...

Have you ever used OpenGL?


Like @zamtmn said, you'll have to call one of the  Load_GL_*** 
functions to initialize OpenGL before using it.
Because graphics drivers are very hardware-specific, they're loaded as
dynamic libraries and can vary from host to host. FPC's OpenGL units
declare all API functions as function pointers (initialized to  Nil)
and resolves their actual values only when calling one of the
aforementioned  Load_GL_***  functions, with each variant only
resolving the functions that are required by that version of the
OpenGL specification.

Looking at the OpenGL documentation for  glGenBuffers and scrolling to
the bottom of the page, we can see that it is only supported from
version 2.0 and onwards, so you'll have to call at least 
Load_GL_Version_2_0.

So in essence, the segfault you're getting has nothing to do with 
@VBO, but with the fact that you're calling a function pointer whose
value is  Nil  (if you hover over  glGenBuffers  in Lazarus you'll see
that it is declared as a  var).

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LemonParty · 2024-12-19 11:39

I see. Where can I download a proper DLL?

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zamtmn · 2024-12-19 12:12

>>I see. Where can I download a proper DLL?
No need download dll. You need install drivers from your video card
manuacturer site, not use default ms video driver. and run
Load_GL_version_1_5 (or later if you yse features from later version)
once, before call glGenBuffers

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LemonParty · 2024-12-19 12:44

I have installed drivers and Load_GL_version_2_0 return false. I see
from source code of GLext that opengl32.dll is used when
Load_GL_version_* called.

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zamtmn · 2024-12-19 13:22

You must call Load_GL_versionХХХ after create OpenGL context. What GL
control you use? TOpenglControl?

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LemonParty · 2024-12-19 13:55

I using glfw. I moved Load_GL_version_2_0 after
glfwMakeContextCurrent(window); and now it works. Thank you.

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Mathias · 2025-01-09 17:04

Quote from: LemonParty on December 19, 2024, 02:55:27 pmI using glfw.
I moved Load_GL_version_2_0 after glfwMakeContextCurrent(window); and
now it works. Thank you.
The order is very important.