Chisel/src/main/java/com/cricketcraft/chisel/client/gui/GuilScrolledBox.java

package com.cricketcraft.chisel.client.gui;

import net.minecraft.client.Minecraft;
import net.minecraft.client.gui.Gui;
import net.minecraft.client.renderer.Tessellator;

import org.lwjgl.opengl.GL11;

public class GuilScrolledBox extends GuiElement {

	public int offset = 0;
	int contentHeight = 0;
	int scrollingStart = -1;

	public GuilScrolledBox(int x, int y, int w, int h) {
		super(x, y, w, h);
	}

	int x0, x1;

	protected void overlayBackground(int start, int end, int color, int a1, int a2) {
		Tessellator tessellator = Tessellator.instance;

		float f = 32.0F;

		tessellator.startDrawingQuads();
		tessellator.setColorRGBA_I(color, a2);
		tessellator.addVertexWithUV(x0, end, 0.0D, 0.0D, end / f);
		tessellator.addVertexWithUV(x1, end, 0.0D, gui.width / f, end / f);
		tessellator.setColorRGBA_I(color, a1);
		tessellator.addVertexWithUV(x1, start, 0.0D, gui.width / f, start / f);
		tessellator.addVertexWithUV(x0, start, 0.0D, 0.0D, start / f);
		tessellator.draw();
	}

	@Override
	public GuiElement addChild(GuiElement e) {
		int childBottom = e.y + e.h - 18;
		if (childBottom > contentHeight)
			contentHeight = childBottom;

		return super.addChild(e);
	}

	@Override
	public void render() {
		GL11.glColor4f(1.0F, 1.0F, 1.0F, 1.0F);
		Minecraft.getMinecraft().getTextureManager().bindTexture(Gui.optionsBackground);
		x0 = -gui.screenX;
		x1 = -gui.screenX + gui.width;

		overlayBackground(y, h, 0x202020, 0xff, 0xff);

		GL11.glPushMatrix();
		GL11.glTranslatef(0.0f, offset, 0.0f);
		super.render();
		GL11.glPopMatrix();

		GL11.glEnable(GL11.GL_BLEND);
		GL11.glBlendFunc(GL11.GL_SRC_ALPHA, GL11.GL_ONE_MINUS_SRC_ALPHA);
		GL11.glDisable(GL11.GL_ALPHA_TEST);
		GL11.glShadeModel(GL11.GL_SMOOTH);
		GL11.glDisable(GL11.GL_TEXTURE_2D);
		overlayBackground(y, y + 8, 0x000000, 0xff, 0x00);
		overlayBackground(h - 8, h, 0x000000, 0x00, 0xff);
		GL11.glEnable(GL11.GL_TEXTURE_2D);
		GL11.glShadeModel(GL11.GL_FLAT);
		GL11.glEnable(GL11.GL_ALPHA_TEST);
		GL11.glDisable(GL11.GL_BLEND);

		Minecraft.getMinecraft().getTextureManager().bindTexture(Gui.optionsBackground);
		overlayBackground(-gui.screenY, y, 0x404040, 0xff, 0xff);
		overlayBackground(h, -gui.screenY + gui.height, 0x404040, 0xff, 0xff);
	}

	@Override
	public void mouseMove(InputMouseEvent ev) {
		if (scrollingStart != -1) {
			offset = ev.y - scrollingStart;
			if (offset > contentHeight)
				offset = contentHeight;
			if (offset < -contentHeight)
				offset = -contentHeight;
		}

		ev.y -= offset;
		super.mouseMove(ev);
		ev.y += offset;
	}

	@Override
	public void mouseDown(InputMouseEvent ev) {
		scrollingStart = ev.y - offset;

		if (ev.y >= y && ev.y < y + h) {
			ev.y -= offset;
			super.mouseDown(ev);
			ev.y += offset;
		}
	}

	@Override
	public void mouseUp(InputMouseEvent ev) {
		scrollingStart = -1;

		if (ev.y >= y && ev.y < y + h) {
			ev.y -= offset;
			super.mouseUp(ev);
			ev.y += offset;
		}
	}
}