Leaning Technologies•7mo ago

Need help with basic LWJGL 2.9.0 demo loading on CheerpJ

Hello, I am trying to get a very simple LWJGL 2.9.0 Demo working via CheerpJ, but am running into an error Error: window.lwjglCanvasElement is not set or is not a canvas. I've attached a picture of my project structure as well as the the error itself and some other relavent things. My desktop application is a NetBeans project using JDK 8. Here's the source code of the triangle that I found online:

package org.nemotech.opengl;

import org.lwjgl.LWJGLException;
import org.lwjgl.opengl.Display;
import org.lwjgl.opengl.DisplayMode;
import org.lwjgl.opengl.GL11;

public class Main {
    
    public static void main(String[] args) {
        
        try {
            Display.setDisplayMode(new DisplayMode(800, 600));
            Display.setTitle("Triangle Example");
            Display.create();
        } catch (LWJGLException e) {
            e.printStackTrace();
            System.exit(1);
        }

        // Initialize OpenGL
        GL11.glMatrixMode(GL11.GL_PROJECTION);
        GL11.glLoadIdentity();
        GL11.glOrtho(0, 800, 0, 600, 1, -1);
        GL11.glMatrixMode(GL11.GL_MODELVIEW);

        while (!Display.isCloseRequested()) {
            // Clear the screen
            GL11.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT);

            // Draw a triangle
            GL11.glBegin(GL11.GL_TRIANGLES);
            GL11.glColor3f(1.0f, 0.0f, 0.0f); // Red
            GL11.glVertex2f(400, 100);
            GL11.glColor3f(0.0f, 1.0f, 0.0f); // Green
            GL11.glVertex2f(100, 500);
            GL11.glColor3f(0.0f, 0.0f, 1.0f); // Blue
            GL11.glVertex2f(700, 500);
            GL11.glEnd();

            Display.update();
        }

        Display.destroy();
    }
    
}

package org.nemotech.opengl;

import org.lwjgl.LWJGLException;
import org.lwjgl.opengl.Display;
import org.lwjgl.opengl.DisplayMode;
import org.lwjgl.opengl.GL11;

public class Main {
    
    public static void main(String[] args) {
        
        try {
            Display.setDisplayMode(new DisplayMode(800, 600));
            Display.setTitle("Triangle Example");
            Display.create();
        } catch (LWJGLException e) {
            e.printStackTrace();
            System.exit(1);
        }

        // Initialize OpenGL
        GL11.glMatrixMode(GL11.GL_PROJECTION);
        GL11.glLoadIdentity();
        GL11.glOrtho(0, 800, 0, 600, 1, -1);
        GL11.glMatrixMode(GL11.GL_MODELVIEW);

        while (!Display.isCloseRequested()) {
            // Clear the screen
            GL11.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT);

            // Draw a triangle
            GL11.glBegin(GL11.GL_TRIANGLES);
            GL11.glColor3f(1.0f, 0.0f, 0.0f); // Red
            GL11.glVertex2f(400, 100);
            GL11.glColor3f(0.0f, 1.0f, 0.0f); // Green
            GL11.glVertex2f(100, 500);
            GL11.glColor3f(0.0f, 0.0f, 1.0f); // Blue
            GL11.glVertex2f(700, 500);
            GL11.glEnd();

            Display.update();
        }

        Display.destroy();
    }
    
}

Solution:

1. add this HTML to the start of the document body

<canvas id="lwjgl" width="800" height"600"></canvas>

<canvas id="lwjgl" width="800" height"600"></canvas>

2. to the script, add the following line before the cheerpjRunMain call:...

Jump to solution

57 Replies

seanOP•7mo ago

Here are the VM options I am using (just links native LWJGL binaries):

-Djava.library.path="/Users/sean/Documents/lwjgl-2.9.0/native/macosx"

-Djava.library.path="/Users/sean/Documents/lwjgl-2.9.0/native/macosx"

Here is my index.html page:

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>LWJGL Test</title>
    <script src="https://cjrtnc.leaningtech.com/3.0/cj3loader.js"></script>
  </head>
  <body style="background-color:#D3D3D3;">
      <script>
          (async function () {
            await cheerpjInit({
              version: 8,
              javaProperties: ["java.library.path=/app/cheerpj-natives/natives", "org.lwjgl.util.NoChecks=true"],
            });
            cheerpjCreateDisplay(800, 600);
            await cheerpjRunMain(
              "org.nemotech.opengl.Main",
              "/app/OpenGLTest.jar:/app/lwjgl-2.9.0.jar:/app/lwjgl_util-2.9.0.jar"
            );
          })();
      </script>
      <pre id="console"/>
  </body>
</html>

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>LWJGL Test</title>
    <script src="https://cjrtnc.leaningtech.com/3.0/cj3loader.js"></script>
  </head>
  <body style="background-color:#D3D3D3;">
      <script>
          (async function () {
            await cheerpjInit({
              version: 8,
              javaProperties: ["java.library.path=/app/cheerpj-natives/natives", "org.lwjgl.util.NoChecks=true"],
            });
            cheerpjCreateDisplay(800, 600);
            await cheerpjRunMain(
              "org.nemotech.opengl.Main",
              "/app/OpenGLTest.jar:/app/lwjgl-2.9.0.jar:/app/lwjgl_util-2.9.0.jar"
            );
          })();
      </script>
      <pre id="console"/>
  </body>
</html>

I am using

npx http-server -p 8080

npx http-server -p 8080

for the local HTTP server

seanOP•7mo ago

apignotti•7mo ago

You need to simply initialize the global variable lwjglCanvasElement to the HTML5 canvas object that you want to use as your rendering area Please keep in mind that the lwjgl implementation we provide is partial, consider using the browsercraft demo as a guide on how it should be used.

apignotti•7mo ago

https://github.com/leaningtech/browsercraft/blob/main/minecraft-web.js#L179

GitHub

browsercraft/minecraft-web.js at main · leaningtech/browsercraft

Unmodified Minecraft 1.2.5 in the browser using CheerpJ - leaningtech/browsercraft

seanOP•7mo ago

Thanks for the quick response. How should I do this? I know little to nothing regarding HTML/JS

apignotti•7mo ago

There are a few steps, you need to create a <canvas> element, resolve it using getElementById, and assign it with the global variable in JavaScript window.lwjglCanvasElement = getElementById(...). I don't have the opportunity of giving you direct code right now, @Alex please provide some guidance when you can But these are all very basic HTML/JS operations, so it could be a good chance of picking up the basics. You'll find countless tutorials on these.

Alex•7mo ago

hello 👋 as Alessandro suggested, the LWJGL implementation expects you to tell it what canvas to use by setting window.lwjglCanvasElement to an instance of HTMLCanvasElement before you run cheerpjRunMain

Solution

Alex•7mo ago

1. add this HTML to the start of the document body

<canvas id="lwjgl" width="800" height"600"></canvas>

<canvas id="lwjgl" width="800" height"600"></canvas>

2. to the script, add the following line before the cheerpjRunMain call:

window.lwjglCanvasElement = document.getElementById("lwjgl");

window.lwjglCanvasElement = document.getElementById("lwjgl");

Alex•7mo ago

(one of the reasons this is required because any canvases managed by CheerpJ inside the display div use a 2D graphics context. LWJGL’s canvas needs to be 3D - and you can’t use multiple contexts on the same canvas element: https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/getContext) hopefully this helps - @ me if you run into any trouble :)

seanOP•7mo ago

Hey there, thanks for the response. I've edited the page with those 2 steps, but I'm getting a different error now:

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>LWJGL Test</title>
    <script src="https://cjrtnc.leaningtech.com/3.0/cj3loader.js"></script>
  </head>
  <body style="background-color:#D3D3D3;">
      <canvas id="lwjgl"></canvas>
      <script>
          (async function () {
            await cheerpjInit({
              version: 8,
              javaProperties: ["java.library.path=/app/cheerpj-natives/natives", "org.lwjgl.util.NoChecks=true"],
            });
            cheerpjCreateDisplay(800, 600);
            window.lwjglCanvasElement = document.getElementById("lwjgl");
            await cheerpjRunMain(
              "org.nemotech.opengl.Main",
              "/app/OpenGLTest.jar:/app/lwjgl-2.9.0.jar:/app/lwjgl_util-2.9.0.jar"
            );
          })();
      </script>
      <pre id="console"/>
  </body>
</html>

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>LWJGL Test</title>
    <script src="https://cjrtnc.leaningtech.com/3.0/cj3loader.js"></script>
  </head>
  <body style="background-color:#D3D3D3;">
      <canvas id="lwjgl"></canvas>
      <script>
          (async function () {
            await cheerpjInit({
              version: 8,
              javaProperties: ["java.library.path=/app/cheerpj-natives/natives", "org.lwjgl.util.NoChecks=true"],
            });
            cheerpjCreateDisplay(800, 600);
            window.lwjglCanvasElement = document.getElementById("lwjgl");
            await cheerpjRunMain(
              "org.nemotech.opengl.Main",
              "/app/OpenGLTest.jar:/app/lwjgl-2.9.0.jar:/app/lwjgl_util-2.9.0.jar"
            );
          })();
      </script>
      <pre id="console"/>
  </body>
</html>

@Alex

Alex•7mo ago

hm, so it looks like this isn’t going to be as easy as we thought right now, the LWJGL implementation in cheerpj-natives is built so it supports only the functions that Minecraft uses you could try to implement that function (Java_org_…_getRootWindow) inside lwjgl.js

seanOP•7mo ago

Okay I gotcha, I assume just making it a stub function should suffice?

Alex•7mo ago

hopefully…. try returning null

seanOP•7mo ago

Okay :) trying that

Alex•7mo ago

alternatively, since you have access to the Java source you could modify it in such a way that it doesn’t call that method at all (i.e. remove the call to Display.create) my guess would be that you probably don’t need any display things at all actually

seanOP•7mo ago

True, I had assumed that was necessary for CheerpJ, but maybe all Display calls can be omitted

seanOP•7mo ago

Was writing my message as you were writing this, yeah I'll try omitting them for now

Alex•7mo ago

ah, you're also going to need to give the canvas a width and a height:

<canvas id="lwjgl" width="800" height"600"></canvas>

<canvas id="lwjgl" width="800" height"600"></canvas>

seanOP•7mo ago

This happens with all Display code commented out unfortunately, also it seems detached from the CheerpJ frame

seanOP•7mo ago

And adding a

function Java_org_lwjgl_opengl_LinuxDisplay_getRootWindow()
{
    return null;
}

function Java_org_lwjgl_opengl_LinuxDisplay_getRootWindow()
{
    return null;
}

stub to lwjgl.js yields the same previous error message about the LinuxDisplay (with the Display code)

Alex•7mo ago

hmm here's where this is thrown in LWJGL itself: https://github.com/search?q=org%3ALWJGL+%22No+OpenGL+context+found+in+the+current+thread%22&type=code

also it seems detached from the CheerpJ frame

this is expected and fine; just hide the CheerpJ display. here's browsercraft doing exactly that: https://github.com/leaningtech/browsercraft/blob/main/minecraft-web.js#L146-L149

seanOP•7mo ago

Okay gotcha Hmmm

Alex•7mo ago

my thoughts exactly! 😛 give me a minute to look into this more

seanOP•7mo ago

Okay take your time. I really appreciate the help

Alex•7mo ago

OK, it looks like I was wrong here, you do need something Display-y so... I've gone and added LWJGL support to JavaFiddle so we can better test this

Alex•7mo ago

LWJGL test

LWJGL test - JavaFiddle

// Example using LWJGL 2.9.0 // Warning: experimental! import org.lwjgl.LWJGLException; import org.lwjgl.opengl.Display; import org.lwjgl.opengl.DisplayMode; import org.lwjgl.opengl.GL11; public class Main { public static void main(String[] args) { try { Display.setDisplayMode(new DisplayMode(800, 600)); Dis...

Alex•7mo ago

it exhibits the same error you are seeing there must be some other way of initialising GL that Minecraft 1.2.5 uses, since this error doesn't happen in browsercraft

seanOP•7mo ago

Very nice :)

Alex•7mo ago

I'm not familiar enough with LWJGL myself in order to feel confident advising on this. Maybe if we could see how Minecraft does it or alternatively try to implement that stub correctly

seanOP•7mo ago

Yes I think it's definitely the way it initalizes it as well, as I tried using browsercraft source, but I changed downloading the client from Mojang to this JAR instead, which yields the same error

Alex•7mo ago

oh, really? hm

seanOP•7mo ago

Yeah

Alex•7mo ago

that throws my theory out of the window (pun intended)

seanOP•7mo ago

Is that build of minecraft opensource? Well, i suppose it wouldn't be but idk if it's obfuscated

Alex•7mo ago

java tends to be easy to reverse-engineer...

seanOP•7mo ago

I mean I could try analyzing the source code of their client

Alex•7mo ago

it might not be helpful anyway, if this is the case I'll try to implement getRootWindow properly

seanOP•7mo ago

Sounds good Yeah, I was just unsure if they used some sophisticated obfuscation tool such as Zelix Klassmaster, etc

Alex•7mo ago

I don't think they did, no @ayunami2000 knows a bit about reverse-engineering Minecraft, I think, if we want to go down that road

seanOP•7mo ago

OK just looks like very minor obfuscation, such as variable and class renaming. Control flow seems untouched as there's definitely not string encryption either.

seanOP•7mo ago

Now to find the classes that communicate with LWJGL ... Would probably be easy to just use grep to find them, but that's if we really need to see what they did

Alex•7mo ago

update on this: i will need to revisit this another day if thats OK

seanOP•7mo ago

Sure no problem 🙂

Hypex•7mo ago

I wonder if a return 0 would work I'm pretty sure the LWJGL impl just returns 0 for the other get window functions

seanOP•7mo ago

Unfortunately the same thing. Exception in thread "Thread-0" java.lang.UnsatisfiedLinkError: Java_org_lwjgl_opengl_LinuxDisplay_getRootWindow, which is the same as if I don't have the stub at all

seanOP•7mo ago

CheerpJ_LWJGL_2.9.0_...

ayunami2000•7mo ago

Look up MCP For deobfuscating Minecraft

seanOP•7mo ago

Might be overkill at the moment given that I just want to render 8 lines of code for a 2D triangle. I might go down that route for a larger project, once I can get this triangle working

downthecrop•7mo ago

I'd suggest an even simpler example like just changing the glClear color to red. There is no implementation for glVertex2f in the natives.

downthecrop•7mo ago

you can stub out LinuxDisplay_getRootWindow and LinuxDisplay_nSetWindowIcon as suggested above.

Alex•7mo ago

nice! yeah, these just need stubs. happy to take a PR on cheerpj-natives

seanOP•7mo ago

Okay cool, this seems to be working 😎 . Yeah looks like 2d drawing calls aren't implemented yet. I modified the code to draw a small red square (since it looks like quads are supported, but tris are not) with 3F calls instead, but keep running into GL_INVALID_OPERATION: Vertex buffer is not big enough for the draw call. I've tried making vertexBuf larger than 32, but no matter what size I set it to, it results in the same thing. I'll try tinkering around with it some more and see if I have any luck

    public static void main(String[] args) {
        try {
            Display.setDisplayMode(new DisplayMode(1000, 500));
            Display.create();
        } catch (LWJGLException e) {
            e.printStackTrace();
            System.exit(1);
        }

        // Initialize OpenGL
        GL11.glMatrixMode(GL11.GL_PROJECTION);
        GL11.glLoadIdentity();
        GL11.glOrtho(0, 1000, 0, 500, 1, -1);
        GL11.glMatrixMode(GL11.GL_MODELVIEW);

        // Set the clear color to black
        GL11.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

        while (!Display.isCloseRequested()) {
            // Clear the screen
            GL11.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT);
            GL11.glLoadIdentity();

            // Draw a red square
            GL11.glColor3f(1.0f, 0.0f, 0.0f); // Red
            GL11.glBegin(GL11.GL_QUADS);
            GL11.glVertex3f(100, 100, 0); // Top-left
            GL11.glVertex3f(200, 100, 0); // Top-right
            GL11.glVertex3f(200, 200, 0); // Bottom-right
            GL11.glVertex3f(100, 200, 0); // Bottom-left
            GL11.glEnd();

            Display.update();
            Display.sync(60);
        }

        Display.destroy();
    }

    public static void main(String[] args) {
        try {
            Display.setDisplayMode(new DisplayMode(1000, 500));
            Display.create();
        } catch (LWJGLException e) {
            e.printStackTrace();
            System.exit(1);
        }

        // Initialize OpenGL
        GL11.glMatrixMode(GL11.GL_PROJECTION);
        GL11.glLoadIdentity();
        GL11.glOrtho(0, 1000, 0, 500, 1, -1);
        GL11.glMatrixMode(GL11.GL_MODELVIEW);

        // Set the clear color to black
        GL11.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

        while (!Display.isCloseRequested()) {
            // Clear the screen
            GL11.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT);
            GL11.glLoadIdentity();

            // Draw a red square
            GL11.glColor3f(1.0f, 0.0f, 0.0f); // Red
            GL11.glBegin(GL11.GL_QUADS);
            GL11.glVertex3f(100, 100, 0); // Top-left
            GL11.glVertex3f(200, 100, 0); // Top-right
            GL11.glVertex3f(200, 200, 0); // Bottom-right
            GL11.glVertex3f(100, 200, 0); // Bottom-left
            GL11.glEnd();

            Display.update();
            Display.sync(60);
        }

        Display.destroy();
    }

What it looks like rendered on the desktop:

Alex•7mo ago

I think that tri fan and strip should be supported, just not TRIANGLES (it hits a debugger) I had a play about with this this morning and it feels to me that it might be more sensible to look into supporting modern LWJGL3 and OpenGL ES (ie WebGL) instead of trying to hack together a compatibility layer for GL11->WebGL. (alternatively, we do that, but seriously - the current implementation is mostly hacked together just to support a specific version of Minecraft) depends on your usecase @sean. perhaps you could explain what you’re aiming to build in the end?

Hypex•7mo ago

That sounds better, and Minecraft does support LWJGL 3 if you use a patched asset index API Probably not for 1.2.5 tho

seanOP•7mo ago

My long term goal was to port a legacy LWJGL 3d landscape and model editor that I wrote a few years ago for a game I'm working on. I thought it would be really neat to have it browser based

Alex•7mo ago

that sounds cool; let's make a thread in #cheerpj about it not a problem, we only picked that version because it used GL1 iirc

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Need help with basic LWJGL 2.9.0 demo loading on CheerpJ