So I am developing my first (well 2nd really) mod.  I am adding slabs (of wool) and I got it all to work, except for the part that the slabs, the first 8 in the id are laid on the ground, and the other 8 are on the top.  I have no clue what is going wrong...

 

package us.xvicario.minecraft.EssentialStuff.common;

import java.util.List;

import us.xvicario.minecraft.EssentialStuff.common.mod_EssentialStuff;

import cpw.mods.fml.relauncher.Side;
import cpw.mods.fml.relauncher.SideOnly;
import net.minecraft.block.Block;
import net.minecraft.block.material.Material;
import net.minecraft.creativetab.CreativeTabs;
import net.minecraft.entity.Entity;
import net.minecraft.item.ItemStack;
import net.minecraft.util.AxisAlignedBB;
import net.minecraft.util.Facing;
import net.minecraft.world.IBlockAccess;
import net.minecraft.world.World;

public class BlockWoolSlab extends Block {

private final boolean isDoubleSlab;

public BlockWoolSlab(int id, boolean par2) {
	super(id, Material.cloth);
	this.isDoubleSlab = par2;
	setBlockName("woolSlab");
	Block added = setCreativeTab(CreativeTabs.tabBlock);
	System.out.println(added.toString());

	if (par2)
        {
            opaqueCubeLookup[id] = true;
        }
        else
        {
            this.setBlockBounds(0.0F, 0.0F, 0.0F, 1.0F, 0.5F, 1.0F);
        }

        this.setLightOpacity(255);
}

    public void setBlockBoundsBasedOnState(IBlockAccess par1IBlockAccess, int par2, int par3, int par4)
    {
        if (this.isDoubleSlab)
        {
            this.setBlockBounds(0.0F, 0.0F, 0.0F, 1.0F, 1.0F, 1.0F);
        }
        else
        {
            boolean var5 = (par1IBlockAccess.getBlockMetadata(par2, par3, par4) &  != 0;

            if (var5)
            {
                this.setBlockBounds(0.0F, 0.5F, 0.0F, 1.0F, 1.0F, 1.0F);
            }
            else
            {
                this.setBlockBounds(0.0F, 0.0F, 0.0F, 1.0F, 0.5F, 1.0F);
            }
        }
    }
    
    public void setBlockBoundsForItemRender()
    {
        if (this.isDoubleSlab)
        {
            this.setBlockBounds(0.0F, 0.0F, 0.0F, 1.0F, 1.0F, 1.0F);
        }
        else
        {
            this.setBlockBounds(0.0F, 0.0F, 0.0F, 1.0F, 0.5F, 1.0F);
        }
    }
    
    public void addCollidingBlockToList(World par1World, int par2, int par3, int par4, AxisAlignedBB par5AxisAlignedBB, List par6List, Entity par7Entity)
    {
        this.setBlockBoundsBasedOnState(par1World, par2, par3, par4);
        super.addCollidingBlockToList(par1World, par2, par3, par4, par5AxisAlignedBB, par6List, par7Entity);
    }
    
    public boolean isOpaqueCube()
    {
        return this.isDoubleSlab;
    }

    public int func_85104_a(World par1World, int par2, int par3, int par4, int par5, float par6, float par7, float par8, int par9)
    {
        return this.isDoubleSlab ? par9 : (par5 != 0 && (par5 == 1 || (double)par7 <= 0.5D) ? par9 : par9 | ;
    }
    
    @Override
    public int damageDropped(int par1)
    {
        return par1;
    }

    /**
     * If this block doesn't render as an ordinary block it will return False (examples: signs, buttons, stairs, etc)
     */
    public boolean renderAsNormalBlock()
    {
        return this.isDoubleSlab;
    }
    
    public boolean shouldSideBeRendered(IBlockAccess par1IBlockAccess, int par2, int par3, int par4, int par5)
    {
        if (this.isDoubleSlab)
        {
            return super.shouldSideBeRendered(par1IBlockAccess, par2, par3, par4, par5);
        }
        else if (par5 != 1 && par5 != 0 && !super.shouldSideBeRendered(par1IBlockAccess, par2, par3, par4, par5))
        {
            return false;
        }
        else
        {
            int var6 = par2 + Facing.offsetsXForSide[Facing.faceToSide[par5]];
            int var7 = par3 + Facing.offsetsYForSide[Facing.faceToSide[par5]];
            int var8 = par4 + Facing.offsetsZForSide[Facing.faceToSide[par5]];
            boolean var9 = (par1IBlockAccess.getBlockMetadata(var6, var7, var8) &  != 0;
            return var9 ? (par5 == 0 ? true : (par5 == 1 && super.shouldSideBeRendered(par1IBlockAccess, par2, par3, par4, par5) ? true : !isBlockSingleSlab(par1IBlockAccess.getBlockId(par2, par3, par4)) || (par1IBlockAccess.getBlockMetadata(par2, par3, par4) &  == 0)) : (par5 == 1 ? true : (par5 == 0 && super.shouldSideBeRendered(par1IBlockAccess, par2, par3, par4, par5) ? true : !isBlockSingleSlab(par1IBlockAccess.getBlockId(par2, par3, par4)) || (par1IBlockAccess.getBlockMetadata(par2, par3, par4) &  != 0));
        }
    }
    
    @SideOnly(Side.CLIENT)

    /**
     * Takes a block ID, returns true if it's the same as the ID for a stone or wooden single slab.
     */
    private static boolean isBlockSingleSlab(int par0)
    {
        return par0 == mod_EssentialStuff.woolSingleSlab.blockID;
    }

    /**
     * Returns the slab block name with step type.
     */
    //public abstract String getFullSlabName(int var1);

    /**
     * Get the block's damage value (for use with pick block).
     */
    public int getDamageValue(World par1World, int par2, int par3, int par4)
    {
        return super.getDamageValue(par1World, par2, par3, par4) & 7;
    }

    @SideOnly(Side.CLIENT)
    public int idPicked(World par1World, int par2, int par3, int par4) {
        return isBlockSingleSlab(this.blockID) ? this.blockID : (this.blockID == mod_EssentialStuff.woolDoubleSlab.blockID ? Block.stoneSingleSlab.blockID : (this.blockID == Block.woodDoubleSlab.blockID ? Block.woodSingleSlab.blockID : Block.stoneSingleSlab.blockID));
    }
    
@Override
public int getBlockTextureFromSideAndMetadata(int side, int metadata) {
	if (metadata == 0) {
		return 64;
	} else {
            metadata = ~(metadata & 15);
            return 113 + ((metadata &  >> 3) + (metadata & 7) * 16;
	}
}

@SideOnly(Side.CLIENT)
public void getSubBlocks(int unknown, CreativeTabs tab, List subItems) {
	for (int ix = 0; ix < 16; ix++) {
		subItems.add(new ItemStack(this, 1, ix));
	}
}

}

 

If you need any more information, please just ask.

 

edit: I fixed it, but I dont understand the part of the code that determines what the slab is on, If someone can explain it to me.

else
        {
            boolean var5 = (par1IBlockAccess.getBlockMetadata(par2, par3, par4) &  != 0;

            if (var5)
            {
                this.setBlockBounds(0.0F, 0.5F, 0.0F, 1.0F, 1.0F, 1.0F);
            }
            else
            {
                this.setBlockBounds(0.0F, 0.0F, 0.0F, 1.0F, 0.5F, 1.0F);
            }
        }

It's because the minecraft uses metadata to checking if it's on bottom or on top.

You can only use the first 8 metadata because the last 8 metadata is the top one.

You will need two block for wool,one for the first 8 ,one for the last 8.