Im in the progress of making a mod, but one of my machines requires a input of steam, I already have an internal tank and can get the current amount with a simple log, however I would like to see the current amount of fluid in the gui, similar to Thermal Expansion crucible.

Here is my gui for the machine

package com.brady131313.steamreborn.client.gui.machines;

import com.brady131313.steamreborn.inventory.ContainerAlloyCompressor;
import com.brady131313.steamreborn.reference.Names;
import com.brady131313.steamreborn.reference.Textures;
import com.brady131313.steamreborn.tileentity.TileEntityAlloyCompressor;
import cpw.mods.fml.relauncher.Side;
import cpw.mods.fml.relauncher.SideOnly;
import net.minecraft.client.gui.inventory.GuiContainer;
import net.minecraft.entity.player.InventoryPlayer;
import net.minecraft.util.StatCollector;
import org.lwjgl.opengl.GL11;


@SideOnly(Side.CLIENT)
public class GuiAlloyCompressor extends GuiContainer {

    private TileEntityAlloyCompressor tileEntityAlloyCompressor;

    public GuiAlloyCompressor(InventoryPlayer inventoryPlayer, TileEntityAlloyCompressor tileEntityAlloyCompressor) {

        super(new ContainerAlloyCompressor(inventoryPlayer, tileEntityAlloyCompressor));
        this.tileEntityAlloyCompressor = tileEntityAlloyCompressor;
        xSize = 176;
        ySize = 187;
    }

    @Override
    protected void drawGuiContainerForegroundLayer(int x, int y) {

        String containerName = StatCollector.translateToLocal(tileEntityAlloyCompressor.getInventoryName());
        fontRendererObj.drawString(containerName, xSize / 2 - fontRendererObj.getStringWidth(containerName) / 2, 6, 4210752);
        fontRendererObj.drawString(StatCollector.translateToLocal(Names.Containers.VANNILLA_INVENTORY), 8, ySize - 96 + 2, 4210752);
    }

    @Override
    protected void drawGuiContainerBackgroundLayer(float var1, int var2, int var3) {

        GL11.glColor4f(1.0F, 1.0F, 1.0F, 1.0F);
        TileEntityAlloyCompressor entity = new TileEntityAlloyCompressor();

        this.mc.getTextureManager().bindTexture(Textures.Gui.ALLOY_COMPRESSOR);

        int xStart = (width - xSize) / 2;
        int yStart = (height - ySize) / 2;

        this.drawTexturedModalRect(xStart, yStart, 0, 0, xSize, ySize);
        int scaleAdjustment;
        int steamAdjustment;

        if (this.tileEntityAlloyCompressor.getState() == 1) {
            scaleAdjustment = this.tileEntityAlloyCompressor.getBurnTimeRemainingScaled(12);
            this.drawTexturedModalRect(xStart + 45, yStart + 36 + 34 - scaleAdjustment, 176, 12 - scaleAdjustment, 14, scaleAdjustment + 2);
        }

        scaleAdjustment = this.tileEntityAlloyCompressor.getCookProgressScaled(36);
        this.drawTexturedModalRect(xStart + 63 , yStart + 32, 176, 34, scaleAdjustment + 1, 30);


    }

}

Well, as long as the amount you need is in a public field or method somewhere, you can just add another  drawString() method to your foreground layer method. Of course you can also draw things other than strings.  For example if you wanted it as a percentage filled bar you could draw a rectangle and then draw a gradient rectangle on top where the gradient rectangle length show percentage of the steam amount versus max steam amount possible.

Ive tried playing around with the buildcraft source and how they draw the fluid in the combustion engine, however the fluid just never shows up. Since im looking for a little rectangle that fills up with the current fluid instead of just a string of numbers. And whats the difference between drawGuiContainerForegroundLayer, and drawGuiContainerBackgroundLayer.

I have been working the past few days on this in my mod and it was rather simple, what you need to do is add the texture of the fluid to the gui in a separate area similar to the progress bar on the furnace gui and then find out how much is stored from the tileentity and decide the height of it based on that

so basically find the scale like i did with the progress bar and use that to increment the height of the fluid?

 

Thanks man, don't know why I didn't think of that earlier.