Add a scroll panel

Closes #44.

1 files changed, 115 insertions, 0 deletions

diff --git a/src/main/java/io/github/cottonmc/cotton/gui/widget/WScrollPanel.java b/src/main/java/io/github/cottonmc/cotton/gui/widget/WScrollPanel.java
new file mode 100644
index 0000000..bd91f06
--- /dev/null
+++ b/src/main/java/io/github/cottonmc/cotton/gui/widget/WScrollPanel.java
@@ -0,0 +1,115 @@
+package io.github.cottonmc.cotton.gui.widget;
+
+import io.github.cottonmc.cotton.gui.GuiDescription;
+import io.github.cottonmc.cotton.gui.widget.data.Axis;
+import net.minecraft.client.util.math.MatrixStack;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Similar to the JScrollPane in Swing, this widget represents a vertically scrollable list of widgets.
+ *
+ * @since 2.0.0
+ */
+public class WScrollPanel extends WClippedPanel {
+	/**
+	 * The spacing between widgets.
+	 */
+	protected int spacing = 4;
+
+	/**
+	 * The scroll bar of this panel.
+	 */
+	protected WScrollBar scrollBar = new WScrollBar(Axis.VERTICAL);
+
+	private int lastScroll = -1;
+
+	// The list of *all* children as opposed to visible children, excluding the scroll bar.
+	private final List<WWidget> allChildren = new ArrayList<>();
+
+	public WScrollPanel() {
+		scrollBar.setParent(this);
+		children.add(scrollBar);
+	}
+
+	public void add(WWidget widget, int width, int height) {
+		widget.setParent(this);
+		allChildren.add(widget);
+		children.add(widget);
+		if (canResize()) {
+			widget.setSize(width, height);
+		}
+	}
+
+	public void add(WWidget widget) {
+		add(widget, 18, 18);
+	}
+
+	@Override
+	public void paint(MatrixStack matrices, int x, int y, int mouseX, int mouseY) {
+		if (scrollBar.getValue() != lastScroll) {
+			layout();
+			lastScroll = scrollBar.getValue();
+		}
+
+		super.paint(matrices, x, y, mouseX, mouseY);
+	}
+
+	@Override
+	public void layout() {
+		children.clear();
+		scrollBar.setLocation(this.width - scrollBar.getWidth(), 0);
+		scrollBar.setSize(8, this.height);
+
+		int offset = scrollBar.getValue();
+		int height = 0;
+
+		for (int i = 0; i < allChildren.size(); i++) {
+			WWidget child = allChildren.get(i);
+			int minY = height - offset;
+			child.setLocation(0, minY);
+			int maxY = minY + child.getHeight();
+
+			if ((minY >= 0 && minY < getHeight()) || (maxY >= 0 && maxY < getHeight()) || (minY < 0 && maxY >= getHeight())) {
+				children.add(child);
+			}
+
+			if (i != allChildren.size() - 1) {
+				height += spacing;
+			}
+
+			height += child.getHeight();
+		}
+
+		children.add(scrollBar);
+		scrollBar.setWindow(Math.min(height / 4, 18));
+		scrollBar.setMaxValue(height);
+	}
+
+	@Override
+	public void validate(GuiDescription c) {
+		for (WWidget child : allChildren) {
+			child.validate(c);
+		}
+		super.validate(c);
+	}
+
+	@Override
+	public void createPeers(GuiDescription c) {
+		super.createPeers(c);
+		for (WWidget child : allChildren) {
+			child.createPeers(c);
+		}
+	}
+
+	public int getSpacing() {
+		return spacing;
+	}
+
+	public WScrollPanel setSpacing(int spacing) {
+		this.spacing = spacing;
+
+		return this;
+	}
+}