Add a global scissor stack for nested scissor support (#59)

* Add a global scissor stack for nested scissor support

* Fix scissors not having proper dimensions, add check for negatives

4 files changed, 158 insertions, 15 deletions

diff --git a/src/main/java/io/github/cottonmc/cotton/gui/client/CottonClientScreen.java b/src/main/java/io/github/cottonmc/cotton/gui/client/CottonClientScreen.java
index 6808aa1..81ff65a 100644
--- a/src/main/java/io/github/cottonmc/cotton/gui/client/CottonClientScreen.java
+++ b/src/main/java/io/github/cottonmc/cotton/gui/client/CottonClientScreen.java
@@ -10,6 +10,7 @@ import net.minecraft.text.Text;
 import io.github.cottonmc.cotton.gui.GuiDescription;
 import io.github.cottonmc.cotton.gui.widget.WPanel;
 import io.github.cottonmc.cotton.gui.widget.WWidget;
+import org.lwjgl.opengl.GL11;
 
 public class CottonClientScreen extends Screen implements TextHoverRendererScreen {
 	protected GuiDescription description;
@@ -31,7 +32,6 @@ public class CottonClientScreen extends Screen implements TextHoverRendererScree
 	public GuiDescription getDescription() {
 		return description;
 	}
-
 	
 	@Override
 	public void init(MinecraftClient client, int screenWidth, int screenHeight) {
@@ -64,7 +64,10 @@ public class CottonClientScreen extends Screen implements TextHoverRendererScree
 		if (description!=null) {
 			WPanel root = description.getRootPanel();
 			if (root!=null) {
+				GL11.glEnable(GL11.GL_SCISSOR_TEST);
 				root.paint(matrices, left, top, mouseX-left, mouseY-top);
+				GL11.glDisable(GL11.GL_SCISSOR_TEST);
+				Scissors.checkStackIsEmpty();
 			}
 		}
 		
diff --git a/src/main/java/io/github/cottonmc/cotton/gui/client/CottonInventoryScreen.java b/src/main/java/io/github/cottonmc/cotton/gui/client/CottonInventoryScreen.java
index 0b2daa1..b758a97 100644
--- a/src/main/java/io/github/cottonmc/cotton/gui/client/CottonInventoryScreen.java
+++ b/src/main/java/io/github/cottonmc/cotton/gui/client/CottonInventoryScreen.java
@@ -13,6 +13,7 @@ import org.lwjgl.glfw.GLFW;
 
 import io.github.cottonmc.cotton.gui.widget.WPanel;
 import io.github.cottonmc.cotton.gui.widget.WWidget;
+import org.lwjgl.opengl.GL11;
 
 /**
  * A screen for a {@link SyncedGuiDescription}.
@@ -222,7 +223,10 @@ public class CottonInventoryScreen<T extends SyncedGuiDescription> extends Handl
 		if (description!=null) {
 			WPanel root = description.getRootPanel();
 			if (root!=null) {
+				GL11.glEnable(GL11.GL_SCISSOR_TEST);
 				root.paint(matrices, x, y, mouseX-x, mouseY-y);
+				GL11.glDisable(GL11.GL_SCISSOR_TEST);
+				Scissors.checkStackIsEmpty();
 			}
 		}
 	}
diff --git a/src/main/java/io/github/cottonmc/cotton/gui/client/Scissors.java b/src/main/java/io/github/cottonmc/cotton/gui/client/Scissors.java
new file mode 100644
index 0000000..a8f65c8
--- /dev/null
+++ b/src/main/java/io/github/cottonmc/cotton/gui/client/Scissors.java
@@ -0,0 +1,147 @@
+package io.github.cottonmc.cotton.gui.client;
+
+import net.fabricmc.api.EnvType;
+import net.fabricmc.api.Environment;
+import net.minecraft.client.MinecraftClient;
+import org.lwjgl.opengl.GL11;
+
+import java.util.ArrayDeque;
+import java.util.stream.Collectors;
+
+/**
+ * Contains a stack for GL scissors for restricting the drawn area of a widget.
+ *
+ * @since 2.0.0
+ */
+@Environment(EnvType.CLIENT)
+public final class Scissors {
+	private static final ArrayDeque<Frame> STACK = new ArrayDeque<>();
+
+	private Scissors() {
+	}
+
+	/**
+	 * Pushes a new scissor frame onto the stack and refreshes the scissored area.
+	 *
+	 * @param x the frame's X coordinate
+	 * @param y the frame's Y coordinate
+	 * @param width the frame's width in pixels
+	 * @param height the frame's height in pixels
+	 * @return the pushed frame
+	 */
+	public static Frame push(int x, int y, int width, int height) {
+		Frame frame = new Frame(x, y, width, height);
+		STACK.push(frame);
+		refreshScissors();
+
+		return frame;
+	}
+
+	/**
+	 * Pops the topmost scissor frame and refreshes the scissored area.
+	 *
+	 * @throws IllegalStateException if there are no scissor frames on the stack
+	 */
+	public static void pop() {
+		if (STACK.isEmpty()) {
+			throw new IllegalStateException("No scissors on the stack!");
+		}
+
+		STACK.pop();
+		refreshScissors();
+	}
+
+	private static void refreshScissors() {
+		MinecraftClient mc = MinecraftClient.getInstance();
+
+		if (STACK.isEmpty()) {
+			// Just use the full window framebuffer as a scissor
+			GL11.glScissor(0, 0, mc.getWindow().getFramebufferWidth(), mc.getWindow().getFramebufferHeight());
+			return;
+		}
+
+		int x = Integer.MIN_VALUE;
+		int y = Integer.MIN_VALUE;
+		int width = -1;
+		int height = -1;
+
+		for (Frame frame : STACK) {
+			if (x < frame.x) {
+				x = frame.x;
+			}
+			if (y < frame.y) {
+				y = frame.y;
+			}
+			if (width == -1 || x + width > frame.x + frame.width) {
+				width = frame.width - (x - frame.x);
+			}
+			if (height == -1 || y + height > frame.y + frame.height) {
+				height = frame.height - (y - frame.y);
+			}
+		}
+
+		int windowHeight = mc.getWindow().getHeight();
+		double scale = mc.getWindow().getScaleFactor();
+		int scaledWidth = (int) (width * scale);
+		int scaledHeight = (int) (height * scale);
+
+		// Expression for Y coordinate adapted from vini2003's Spinnery (code snippet released under WTFPL)
+		GL11.glScissor((int) (x * scale), (int) (windowHeight - (y * scale) - scaledHeight), scaledWidth, scaledHeight);
+	}
+
+	/**
+	 * Internal method. Throws an {@link IllegalStateException} if the scissor stack is not empty.
+	 */
+	static void checkStackIsEmpty() {
+		if (!STACK.isEmpty()) {
+			throw new IllegalStateException("Unpopped scissor frames: " + STACK.stream().map(Frame::toString).collect(Collectors.joining(", ")));
+		}
+	}
+
+	/**
+	 * A single scissor frame in the stack.
+	 */
+	public static final class Frame implements AutoCloseable {
+		private final int x;
+		private final int y;
+		private final int width;
+		private final int height;
+
+		private Frame(int x, int y, int width, int height) {
+			if (width < 0) throw new IllegalArgumentException("Negative width for a stack frame");
+			if (height < 0) throw new IllegalArgumentException("Negative height for a stack frame");
+
+			this.x = x;
+			this.y = y;
+			this.width = width;
+			this.height = height;
+		}
+
+		/**
+		 * Pops this frame from the stack.
+		 *
+		 * @throws IllegalStateException if: <ul>
+		 *                               <li>this frame is not on the stack, or</li>
+		 *                               <li>this frame is not the topmost element on the stack</li>
+		 *                               </ul>
+		 * @see Scissors#pop()
+		 */
+		@Override
+		public void close() {
+			if (STACK.peekLast() != this) {
+				if (STACK.contains(this)) {
+					throw new IllegalStateException(this + " is not on top of the stack!");
+				} else {
+					throw new IllegalStateException(this + " is not on the stack!");
+				}
+			}
+
+			pop();
+		}
+
+		@Override
+		public String toString() {
+			return "Frame{ at = (" + x + ", " + y + "), size = (" + width + ", " + height + ") }";
+		}
+	}
+}
diff --git a/src/main/java/io/github/cottonmc/cotton/gui/widget/WClippedPanel.java b/src/main/java/io/github/cottonmc/cotton/gui/widget/WClippedPanel.java
index d4cd9f5..531ae85 100644
--- a/src/main/java/io/github/cottonmc/cotton/gui/widget/WClippedPanel.java
+++ b/src/main/java/io/github/cottonmc/cotton/gui/widget/WClippedPanel.java
@@ -1,8 +1,7 @@
 package io.github.cottonmc.cotton.gui.widget;
 
-import net.minecraft.client.MinecraftClient;
+import io.github.cottonmc.cotton.gui.client.Scissors;
 import net.minecraft.client.util.math.MatrixStack;
-import org.lwjgl.opengl.GL11;
 
 /**
  * A panel that is clipped to only render widgets inside its bounds.
@@ -12,20 +11,10 @@ public class WClippedPanel extends WPanel {
 	public void paint(MatrixStack matrices, int x, int y, int mouseX, int mouseY) {
 		if (getBackgroundPainter()!=null) getBackgroundPainter().paintBackground(x, y, this);
 
-		GL11.glEnable(GL11.GL_SCISSOR_TEST);
-		MinecraftClient mc = MinecraftClient.getInstance();
-		int rawHeight = mc.getWindow().getHeight();
-		double scaleFactor = mc.getWindow().getScaleFactor();
-		int scaledWidth = (int) (getWidth() * scaleFactor);
-		int scaledHeight = (int) (getHeight() * scaleFactor);
-
-		// Expression for Y coordinate adapted from vini2003's Spinnery (code snippet released under WTFPL)
-		GL11.glScissor((int) (x * scaleFactor), (int) (rawHeight - (y * scaleFactor) - scaledHeight), scaledWidth, scaledHeight);
-
+		Scissors.push(x, y, width, height);
 		for(WWidget child : children) {
 			child.paint(matrices, x + child.getX(), y + child.getY(), mouseX-child.getX(), mouseY-child.getY());
 		}
-
-		GL11.glDisable(GL11.GL_SCISSOR_TEST);
+		Scissors.pop();
 	}
 }