Converting 2d screen coordinates to a ray.

I'm trying to create functionality to take in a 2d screen coordinate and return the block type at that point, as well as the distance to that block. I've tried this function, but it returns a ray in seemingly a random direction. ScreenWidth and ScreenHeight are the Minecraft window size. (I didn't use the built in inverse function because it was giving the wrong result for some reason. I manually verified.)

public static Vec3 GetRay(float screenX, float screenY, Camera cam) {
		Matrix4f projectionMatrix = getProjectionMatrix();
		Matrix4f viewMatrix = getViewMatrix(cam);
		
		float ndcX = (2.0f * screenX) / ScreenWidth - 1.0f;
		float ndcY = 1.0f - (2.0f * screenY) / ScreenHeight;
		Vector4f screenVector = new Vector4f(ndcX, ndcY, -1.0f, 1.0f);
		
        Matrix4f inversePM = new Matrix4f(projectionMatrix);
        float detPM = inversePM.adjugateAndDet();
        inversePM.multiply(1.0f / detPM);
        screenVector.transform(inversePM);
        
        screenVector.setZ(-1.0f);
        screenVector.setW(0.0f);
        
        Matrix4f inverseVM = new Matrix4f(viewMatrix);
        float detVM = inverseVM.adjugateAndDet();
        inverseVM.multiply(1.0f / detVM);
        screenVector.transform(inverseVM);

        Vec3 direction = new Vec3(screenVector.x(), screenVector.y(), screenVector.z());
        direction = direction.normalize();

        return direction;
    }

private static Matrix4f getViewMatrix(Camera cam) {
        Vec3 cameraPos = cam.getPosition();
        Vector3f camPos = new Vector3f((float) cameraPos.x, (float) cameraPos.y, (float) cameraPos.z);

        Vector3f forward = cam.getLookVector();
        forward.normalize();
        Vector3f up = cam.getUpVector();
        up.normalize();
        Vector3f right = cam.getLeftVector();
        right.mul(-1.0f);
        right.normalize();
        
        float[] values = {
        	right.x(), up.x(), -forward.x(), 0,
        	right.y(), up.y(), -forward.y(), 0,
        	right.z(), up.z(), -forward.z(), 0,
            -camPos.dot(right), -camPos.dot(up), -camPos.dot(forward), 1.0f
        };
        
        Matrix4f viewMatrix = new Matrix4f(values);
        
        return viewMatrix;
    }

private static Matrix4f getProjectionMatrix() {
        double fov = Math.toRadians(90.0);
        double aspectRatio = ScreenWidth / ScreenHeight;
        double nearPlane = 0.05f;
        double farPlane = 1000.0f;

        double yScale = 1.0f / Math.tan(fov / 2.0f);
        double xScale = yScale / aspectRatio;
        double frustumLength = farPlane - nearPlane;

        float[] values = new float[]{
            (float) xScale, 0.0f, 0.0f, 0.0f,
            0.0f, (float) yScale, 0.0f, 0.0f,
            0.0f, 0.0f, (float) -((farPlane + nearPlane) / frustumLength), -1.0f,
            0.0f, 0.0f, (float) -((2.0f * nearPlane * farPlane) / frustumLength), 0.0f
        };

        return new Matrix4f(values);
    }

Edited September 3, 20241 yr by IRaconI