*SOLVED* rendering item icon to bitmap

Hi,

I'm trying to make a little util mod to document all loaded recipes. Currently, I'm stuck at trying to save item icons as images.

I'm thinking of rendering icon to FBO buffer, and then saving it to bitmap. I'm not that good with opengl, so I've tried something simple like that:

https://gist.github.com/trakos/f9a71a5910452c5e14a8

Used like:

MyClass.initFbo();
for (ItemStack item : ItemList.items)
{
     MyClass.renderItem(item);
}

But, obviously it doesn't work - the image is saved, but only the background (glClear) is rendered - the icon is not visible.

Is it the right approach? Any advices on how could I make it work?

Thanks in advance for your time! 

e: if anyone's wondering, I'm using mc 1.6.4.

e2: this works fine when called in tick end after world is loaded:

    static protected void renderItem(ItemStack itemStack)
    {
        if (Tessellator.instance.isDrawing)
        {
            Tessellator.instance.draw();
        }
        GL11.glClearColor(1, 1, 1, 0);
        GL11.glClear(GL11.GL_COLOR_BUFFER_BIT | GL11.GL_DEPTH_BUFFER_BIT);
        GL11.glEnable(GL12.GL_RESCALE_NORMAL);
        drawItemStack(itemStack, 0, 0, "overlay");

        String directory = "C:/test/";
        ScreenShotHelper.saveScreenshot(new File(directory), Minecraft.getMinecraft().displayWidth, Minecraft.getMinecraft().displayHeight);
        moveImageTo(new File(directory + itemStack.getDisplayName() + ".png"), directory);
    }

    protected static RenderItem renderItem = new RenderItem();

    static private void drawItemStack(ItemStack par1ItemStack, int par2, int par3, String par4Str)
    {
        RenderHelper.enableGUIStandardItemLighting();
        renderItem.renderItemAndEffectIntoGUI(Minecraft.getMinecraft().fontRenderer, Minecraft.getMinecraft().getTextureManager(), par1ItemStack, par2, par3);
        //renderItem.renderItemOverlayIntoGUI(Minecraft.getMinecraft().fontRenderer, this.mc.getTextureManager(), par1ItemStack, par2, par3 - (this.draggedStack == null ? 0 : , par4Str);
        RenderHelper.disableStandardItemLighting();
    }

(moveImageTo just renames the file, and the window needs to have desired icon size)

imports:

import net.minecraft.client.Minecraft;
import net.minecraft.util.ScreenShotHelper;
import net.minecraft.item.ItemStack;
import net.minecraft.client.renderer.RenderHelper;
import net.minecraft.client.renderer.Tessellator;
import net.minecraft.client.renderer.entity.RenderItem;
import java.io.File;
import java.io.FilenameFilter;