I made a custom button, which sizes its texture to 1/15 of the Screen.
After that, I tried to also do this with the width and height of the button so that they are equally big.

But the Problem is that the texture gets cut off if I do that.

I will Show you my Gui and Button class:

package armamenthaki.duelmonsters.gui;

import armamenthaki.duelmonsters.util.Log;
import net.minecraft.client.Minecraft;
import net.minecraft.client.gui.GuiButton;
import net.minecraft.client.renderer.GlStateManager;
import net.minecraft.util.ResourceLocation;

public class Button extends GuiButton
{
	private ResourceLocation resource;
	private float scaleFactor;
	
	public Button(int id, float sF, int xPos, int yPos, int width, int height, String str, ResourceLocation pResource)
	{
		super(id, xPos, yPos, width, height, str);
		this.resource = pResource;
		this.scaleFactor = sF;
		this.visible = true;
		this.width = width;
		this.height = height;
	}
	
	public void drawScreen(Minecraft mc)
    {
        if (this.visible)
        { 
        	GlStateManager.pushMatrix();
            mc.renderEngine.bindTexture(this.resource);
            GlStateManager.scale(this.scaleFactor, this.scaleFactor, 1.0);
            this.drawModalRectWithCustomSizedTexture(this.xPosition, this.yPosition, 0, 0, this.width, this.height, 256, 373);
            GlStateManager.popMatrix();
        }
    }
	
	public int getId()
	{
		return this.id;
	}
	
}

package armamenthaki.duelmonsters.gui;

import java.util.ArrayList;

import armamenthaki.duelmonsters.duel.Card;
import armamenthaki.duelmonsters.duel.cards.CardSpeedWarrior;
import armamenthaki.duelmonsters.individual.capabilities.DuelDataProvider;
import armamenthaki.duelmonsters.util.Log;
import net.minecraft.client.gui.GuiButton;
import net.minecraft.client.gui.GuiScreen;
import net.minecraft.client.gui.ScaledResolution;
import net.minecraft.client.renderer.GlStateManager;
import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.util.ResourceLocation;

public class GuiDeckEditor extends GuiScreen
{
	private ArrayList<Card> displayedCards = new ArrayList<Card>();
	private ArrayList<Card> playerCards = new ArrayList<Card>();
	
	
	private static final ResourceLocation cmbase = new ResourceLocation("duelmonsters", "textures/textures/gui/guicmbase.png");
	private Button button1;
	
	public GuiDeckEditor(EntityPlayer player)
	{
		if(!player.world.isRemote)
		{
			playerCards = player.getCapability(DuelDataProvider.DUELDAT_CAP, null).getPlayerCards();
		}
		displayedCards.add(new CardSpeedWarrior());
	}
	
	@Override
    public void drawScreen(int mouseX, int mouseY, float partialTicks)
	{
		for(GuiButton button : this.buttonList)
		{
			if(button instanceof Button)
			{
				((Button) button).drawScreen(mc);
			}
		}
	}
    
	@Override
    public void initGui()
    {
		int id = 0;
		for(Card itCard : displayedCards) 
		{
			float x = (float)width/256;
			x = x/15;
			ResourceLocation resource = itCard.getResource();
			float y = x*256;
			float z = x*373;
			int j = (int)y;
			int k = (int)z;
			Log.getLogger().info(j);
			Log.getLogger().info(k);
			Log.getLogger().info(x);
			Log.getLogger().info(y);
			Log.getLogger().info(z);
			GuiButton button = new Button(id, x, 0, 0, j, k,  "", resource);
			this.buttonList.add(button);
			id++;
		}
		
    }
}

 

Everything works fine, I get no Errors but if I then go ingame, I get this:

(Upper left of the Picture, it should actually show all of the card)

Actually just figured out that I was drawing the Rect related to the buttons' texture, so I changed the
Parameters of the drawRectMethod from this.width and this.height to the original texture size,

and it works.

Sorry for posting, but I was trying it some time already.