2d end void effect - credit to @chylex for inspiration

effect.java

	private static final ResourceLocation texPortalSky = new ResourceLocation("textures/environment/end_sky.png");
	private static final ResourceLocation texPortal = new ResourceLocation("textures/entity/end_portal.png");
	private static final Random consistentRandom = new Random(31100L);
    
	public void drawCenteredEndEffect(int x, int y, int width, int height, float scale) {
		drawEndEffect(x-(width/2), y-(height/2), width, height, scale);
	}
	
	public void drawEndEffect(int x, int y, int width, int height, float scale) {
		consistentRandom.setSeed(31100L);
		Minecraft.getMinecraft().getTextureManager().bindTexture(texPortalSky);
		float baseScale = 1.0f/scale;
		
		GL11.glMatrixMode(GL11.GL_TEXTURE);
		GL11.glPushMatrix();
		GL11.glScalef(4F,4F,1F);

		GL11.glColor4f(0.1f,0.1f,0.1f,1F);
    		this.drawTexturedModalRect(x, y, 0, 0, width, height);
		GL11.glPopMatrix();
		
		GL11.glPushMatrix();
		GL11.glEnable(GL11.GL_BLEND);
		GL11.glBlendFunc(GL11.GL_ONE,GL11.GL_ONE);
		for(int layer = 0; layer < 16; ++layer){
			float revLayer = (16-layer), layerMp = 1F+(layer*0.4F), colorMultiplier = 1F/(revLayer+1F);
			scale = baseScale*0.2F;

		  	Minecraft.getMinecraft().getTextureManager().bindTexture(texPortal);
			GL11.glMatrixMode(GL11.GL_TEXTURE);
			GL11.glPushMatrix();
	
			GL11.glTranslatef(0F,layerMp*(Minecraft.getSystemTime()%400000L)/400000F,0F);
			GL11.glScalef(scale,scale,1F);
			GL11.glRotatef((layer*layer+layer*9)*4F+180F,0F,0F,1F);
			GL11.glScalef(4F,4F,1F);
			
			float red = consistentRandom.nextFloat()*0.5F+0.1F;
			float green = consistentRandom.nextFloat()*0.5F+0.4F;
			float blue = consistentRandom.nextFloat()*0.5F+0.5F;
	
			GL11.glColor4f(red*colorMultiplier,green*colorMultiplier,blue*colorMultiplier,1F);
			this.drawTexturedModalRect(x, y, 0, 0, width, height);
			GL11.glPopMatrix();
		}
		GL11.glPopMatrix();
	}