GuiModListScroll.java

package codechicken.core;

import codechicken.core.launch.CodeChickenCorePlugin;
import codechicken.lib.gui.GuiDraw;
import codechicken.lib.render.RenderUtils;
import codechicken.lib.vec.Rectangle4i;
import net.minecraft.client.renderer.GlStateManager;
import net.minecraft.util.ResourceLocation;
import net.minecraftforge.fml.client.GuiModList;
import net.minecraftforge.fml.common.FMLCommonHandler;
import net.minecraftforge.fml.common.ModContainer;
import net.minecraftforge.fml.common.ModMetadata;
import org.lwjgl.BufferUtils;
import org.lwjgl.input.Keyboard;

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.LinkedList;
import java.util.List;

import static org.lwjgl.opengl.GL11.*;

public class GuiModListScroll {
    private static List<ModContainer> scrollMods = new LinkedList<ModContainer>();

    public static void register(Object mod) {
        register(FMLCommonHandler.instance().findContainerFor(mod));
    }

    private static void register(ModContainer mod) {
        if (!RenderUtils.checkEnableStencil()) {
            CodeChickenCorePlugin.logger.error("Unable to do mod description scrolling due to lack of stencil buffer");
        } else {
            scrollMods.add(mod);
        }
    }

    private static void screenshotStencil(int x) {
        Dimension d = GuiDraw.displayRes();
        ByteBuffer buf = BufferUtils.createByteBuffer(d.width * d.height);
        BufferedImage img = new BufferedImage(d.width, d.height, BufferedImage.TYPE_INT_RGB);

        glPixelStorei(GL_PACK_ALIGNMENT, 1);
        glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
        glReadPixels(0, 0, d.width, d.height, GL_STENCIL_INDEX, GL_UNSIGNED_BYTE, buf);
        for (int i = 0; i < d.width; i++) {
            for (int j = 0; j < d.height; j++) {
                img.setRGB(i, d.height - j - 1, buf.get(j * d.width + i) == 0 ? 0 : 0xFFFFFF);
            }
        }
        try {
            ImageIO.write(img, "png", new File("stencil" + x + ".png"));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static ModContainer lastMod;
    private static double scroll;
    private static double lastFrameTime;
    private static double timeStart;

    public static void draw(GuiModList gui, int mouseX, int mouseY) {
        ModContainer selectedMod = ReflectionManager.getField(GuiModList.class, ModContainer.class, gui, "selectedMod");
        if (selectedMod != lastMod) {
            lastMod = selectedMod;
            scroll = 0;
            timeStart = ClientUtils.getRenderTime();
        }
        if (!scrollMods.contains(selectedMod) || selectedMod.getMetadata().autogenerated) {
            return;
        }

        int y1 = calcDescY(gui, selectedMod);
        int y1draw = y1 + 10;
        int y2 = gui.height - 38;
        int x1 = ReflectionManager.getField(GuiModList.class, Integer.class, gui, "listWidth") + 20;
        int x2 = gui.width - 20;
        if (x2 - x1 <= 20) {
            return;
        }

        glEnable(GL_STENCIL_TEST);
        glStencilFunc(GL_ALWAYS, 1, 1);
        GlStateManager.colorMask(false, false, false, false);
        glStencilOp(GL_ZERO, GL_ZERO, GL_ZERO);
        GuiDraw.drawRect(0, 0, gui.width, gui.height, -1);//clear stencil buffer

        screenshotStencil(1);

        glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);
        GuiDraw.drawRect(x1, y1, gui.width - x1, gui.height - y1, -1);//add description area (even below button)
        glStencilOp(GL_ZERO, GL_ZERO, GL_ZERO);
        GuiDraw.drawRect(gui.width / 2 - 75, y2, 200, 20, -1);//subtract done button

        screenshotStencil(2);

        GlStateManager.colorMask(true, true, true, true);
        glStencilFunc(GL_EQUAL, 1, 1);
        glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);

        gui.drawDefaultBackground();//fill stencil with background

        GlStateManager.colorMask(false, false, false, false);
        glStencilOp(GL_ZERO, GL_ZERO, GL_ZERO);
        GuiDraw.drawRect(0, 0, gui.width, gui.height, -1);
        glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);
        GuiDraw.drawRect(x1, y1draw, x2 - x1, y2 - y1draw, -1);

        screenshotStencil(3);

        GlStateManager.colorMask(true, true, true, true);
        glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);

        String description = selectedMod.getMetadata().description;
        int height = GuiDraw.fontRenderer.listFormattedStringToWidth(description, x2 - x1).size() * GuiDraw.fontRenderer.FONT_HEIGHT;

        boolean needsScroll = height > y2 - y1draw;
        if ((ClientUtils.getRenderTime() - timeStart) > 40 && needsScroll) {
            double dt = ClientUtils.getRenderTime() - lastFrameTime;
            if (new Rectangle4i(x1, y1draw, x2 - x1, y2 - y1draw).contains(mouseX, mouseY)) {
                double d = Keyboard.isKeyDown(Keyboard.KEY_UP) ? -1 : Keyboard.isKeyDown(Keyboard.KEY_DOWN) ? 1 : 0;
                scroll += d * dt * 1.5;
            } else {
                scroll += dt * 0.2;
            }
        }
        lastFrameTime = ClientUtils.getRenderTime();

        //draw description

        double dy = scroll % (height + 20);
        GlStateManager.pushMatrix();
        GlStateManager.translate(0, -dy, 0);
        GuiDraw.fontRenderer.drawSplitString(description, x1, y1draw, x2 - x1, 0xDDDDDD);
        if (needsScroll) {
            GlStateManager.translate(0, height + 20, 0);
            GuiDraw.fontRenderer.drawSplitString(description, x1, y1draw, x2 - x1, 0xDDDDDD);
        }
        GlStateManager.popMatrix();

        glDisable(GL_STENCIL_TEST);
    }

    /**
     * Does not add the last 10 px space before the description normally starts
     * Ignores empty child mods expecting a background draw overwrite
     */
    private static int calcDescY(GuiModList gui, ModContainer mod) {
        ModMetadata meta = mod.getMetadata();
        int y = 35;
        if (!!meta.logoFile.isEmpty() && ReflectionManager.getField(GuiModList.class, ResourceLocation.class, gui, "cachedLogo") != null) {
            y += 65;
        }
        y += 12; // title
        y += 40; // necessary lines
        if (!meta.credits.isEmpty()) {
            y += 10;
        }
        if (!meta.childMods.isEmpty()) {
            y += 10;
        }
        return y;
    }
}