I'm making an addon to IC2, and I need to make a chargeable item (eu) that also holds plasma (I have a way to charge it).  I think a need to implement IElectricItem and IItemHudInfo, but I also think I need to mess with how the itemStack renders (with two damage bars instead on one), which I have no idea how to do.  Any help will be appreciated.

You can't store 2 damage values on a weapon. The damage value is  123:1234/ItemID:DamageValue The only way I know of is NBT data. So look up some tutorials on that. Unfortunately it increases the complication by a large amount. But thats what you have to do. As for the rendering, you would have to look into the openGL, create your own custom renderer for the bars , which shouldn't be too hard. Unless you mean add two numbers to the item in the inventory slot. Which is a little bit different. I'm not sure on any of the IC2 specific stuff though.

I already have both the values I need (through item nbt) I just need the renderer.  I think I need to implement IItemRenderer and use MinecraftForgeClient.registerItemRenderer(), but how do I draw an overlay?  Also, do you know where I can find some tutorials on drawing with OpenGL, because I have absolutely no experience?

MinecraftForgeClient.registerItemRenderer(...) ?

Create a class implementing IItemRenderer

 

register it with:

 

MinecraftForgeClient.registerItemRenderer(int itemID, IItemRenderer renderer);.

 

 

your IItemRenderer class will have several methods to define, one of which is the important one:

 

@Override

public void renderItem(ItemRenderType type, ItemStack item, Object... data)

  {

  //do your render stuff here...you will need to render your own icon, use openGL draw calls to render the damage-bars.

  //you can render...well...pretty much anything here

  }

 

the Object... data  input array contains information such as the World, delta-tick time...etc...it varies by render-type.

 

the other methods help determine _when_ to use the custom renderer.

 

Got that, but do you know of any OpenGL drawing tutorials?

Using LWJGL OpenGL is very complicated when it's your first time.

 

I will help you a little bit :

To render you have the option : use Minecraft Tesselator or use directly OpenGL.

 

With Minecraft Tesselator :

Tesselator t = Tesselator.instance

after to draw use :

t.startDrawingQuads(); // Starts drawing an OpenGL quad

t.addVertex(x, y, z); // Adds a vertex to your quad. Your quad need 4 verticies to be rendered, otherwise you will throm some OpenGL Rendering errors.

t.draw(); // Send your verticies to OpenGL and let your GPU renders it at your screen !

 

Example : Renders the StoneLine Rolplay decorative bar :

                glDisable(GL_TEXTURE_2D);

glEnable(GL_BLEND);

glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

glColor4f(0, 0, 0, 26);

                Tessellator t = Tessellator.instance;

t.startDrawingQuads();

t.addVertex(0, 0, 0);

t.addVertex(0, 20, 0);

t.addVertex(Minecraft.getMinecraft().displayWidth, 20, 0);

t.addVertex(Minecraft.getMinecraft().displayWidth, 0, 0);

t.draw();

 

With OpenGL directly :

Replace uses of Tesselator by glVertex3f (not glVertex2f : that will crash OpenGL due to 3D game not 2D game)

glBegin(GL_QUADS); // Starts drawing an OpenGL quad

glVertex3f(x, y, z); // Like tesselator.addVertex, you need to call that 4 times because you have 4 angles in your quad otherwise it's not a quad !

glEnd(); // Send your verticies to your Graphic card and let your screen display that !

 

 

If you don't know what is vertex, i'm sorry but vertex is the BASE of all games ! Don't hope you will arrive to make good mods without knowing what is vertices ! A vertex represents the coords of angles of an object to render (it not mean colision ; colision are math algoryth to check if an object vertex is touching another object vertex).