Why is this glClear call leading to a runtime Error in Scala-CodePudding

I am trying to create a window, open it and be able to close it and the program should stop after I closed the window.

The Code i wrote so far is mostly copied from this video: Setting Up OpenGL and creating a window

Here is my code:

Window.scala

// The Window displaying the rendered image with openGL
package Main
import org.lwjgl.*;
import org.lwjgl.glfw.*;
import org.lwjgl.opengl.*;
import org.lwjgl.system.*;

import java.nio.*;

import org.lwjgl.glfw.Callbacks.*;
import org.lwjgl.glfw.GLFW.*;
import org.lwjgl.opengl.GL11.*;
import org.lwjgl.system.MemoryStack.*;
import org.lwjgl.system.MemoryUtil.*;

class Window(width: Int, height: Int, name: CharSequence) {

  // Code from https://www.lwjgl.org/guide

  GLFWErrorCallback.createPrint(System.err).set();
  if (!glfwInit()) {
    throw new IllegalStateException("Can't create window")
  }

  var window = glfwCreateWindow(width, height, name, 0, 0);

  glfwMakeContextCurrent(window);

  while (!glfwWindowShouldClose(window)) {

    // glClear(GL_COLOR_BUFFER_BIT);

    glfwSwapBuffers(window);

    glfwPollEvents();

  }

  glfwTerminate();

}

Main.scala:

import Main._
@main def hello: Unit = {
  val window = Window(250,250, "Test");
}

I am using sbt version 1.7.2 to compile and run my code with the build.sbt:

import scala.collection.immutable.Seq
val scala3Version = "3.2.0"

lazy val root = project
  .in(file("."))
  .settings(
    name := "2DRenderer",
    version := "0.1.0-SNAPSHOT",
    scalaVersion := scala3Version,
    libraryDependencies  = "org.scalameta" %% "munit" % "0.7.29" % Test
  )

lazy val lwjglVersion = "3.2.1"

lazy val os = Option(System.getProperty("os.name", ""))
  .map(_.substring(0, 3).toLowerCase) match {
  case Some("win") => "windows"
  case Some("mac") => "macos"
  case _           => "linux"
}

libraryDependencies   = Seq(
  "org.lwjgl" % "lwjgl" % lwjglVersion,
  "org.lwjgl" % "lwjgl-opengl" % lwjglVersion,
  "org.lwjgl" % "lwjgl-glfw" % lwjglVersion,
  "org.lwjgl" % "lwjgl-stb" % lwjglVersion,
  "org.lwjgl" % "lwjgl-assimp" % lwjglVersion,
  "org.lwjgl" % "lwjgl-nanovg" % lwjglVersion,
  "org.lwjgl" % "lwjgl" % lwjglVersion classifier s"natives-$os",
  "org.lwjgl" % "lwjgl-opengl" % lwjglVersion classifier s"natives-$os",
  "org.lwjgl" % "lwjgl-glfw" % lwjglVersion classifier s"natives-$os",
  "org.lwjgl" % "lwjgl-stb" % lwjglVersion classifier s"natives-$os",
  "org.lwjgl" % "lwjgl-assimp" % lwjglVersion classifier s"natives-$os",
  "org.lwjgl" % "lwjgl-nanovg" % lwjglVersion classifier s"natives-$os"
)

fork := true

The code is running fine as long as I do not clear the Color Buffer with glClear(GL_COLOR_BUFFER_BIT). Running the code with clearing the buffer the loop, i get the following error message from sbt:

[info] running (fork) hello
[info] FATAL ERROR in native method: Thread[main,5,main]: No context is current or a function that is not available in the current context was called. The JVM will abort execution.        
[info]  at org.lwjgl.opengl.GL11C.glClear(Native Method)
[info]  at org.lwjgl.opengl.GL11.glClear(GL11.java:1045)
[info]  at Main.Window.<init>(Window.scala:31)
[info]  at Main$package$.hello(Main.scala:3)
[info]  at hello.main(Main.scala:2)
[error] Nonzero exit code returned from runner: 1
[error] (Compile / run) Nonzero exit code returned from runner: 1
[error] Total time: 1 s, completed 05.11.2022 12:58:36

Does anybody know why clearing the color buffer is resulting in this runtime error?

CodePudding user response：

The problem is not doing the glClear. The problem is, that you don't get a OpenGL context in the first place. See the log output:

[info] FATAL ERROR in native method: Thread[main,5,main]: No context is current or a function that is not available in the current context was called. The JVM will abort execution.

This can happen e.g. if working remotely on a machine. Another cause is, that no OpenGL drivers are installed.

CodePudding user response：

The problem is not the glClear call but that I was not setting up the context correctly. According to the LWJGL wiki you can not call any function (i think this means gl_ functions) when you did not create the context like this:

glfwMakeContextCurrent(window);
GL.createCapabilities();

This solved my problem.