From 7a2e6c63c1187eaa2c472adea105f57dec676e86 Mon Sep 17 00:00:00 2001
From: Evan Debenham <Evan@ShatteredPixel.com>
Date: Fri, 26 Aug 2016 18:16:09 -0400
Subject: [PATCH] v0.4.2: vertex buffers now support selective updating

---
 .../java/com/watabou/glwrap/Vertexbuffer.java | 45 ++++++++++++++-----
 1 file changed, 35 insertions(+), 10 deletions(-)

diff --git a/SPD-classes/src/main/java/com/watabou/glwrap/Vertexbuffer.java b/SPD-classes/src/main/java/com/watabou/glwrap/Vertexbuffer.java
index de2de3815..c9204df51 100644
--- a/SPD-classes/src/main/java/com/watabou/glwrap/Vertexbuffer.java
+++ b/SPD-classes/src/main/java/com/watabou/glwrap/Vertexbuffer.java
@@ -30,7 +30,7 @@ public class Vertexbuffer {
 
 	private int id;
 	private FloatBuffer vertices;
-	private boolean needsUpdate;
+	private int updateStart, updateEnd;
 
 	private static ArrayList<Vertexbuffer> buffers = new ArrayList<>();
 
@@ -42,24 +42,49 @@ public class Vertexbuffer {
 		this.vertices = vertices;
 		buffers.add(this);
 
-		//forces an update so the GL data isn't blank
-		needsUpdate = true;
-		updateGLData();
+		updateStart = 0;
+		updateEnd = vertices.limit();
 	}
 
+	//For flagging the buffer for a full update without changing anything
+	public void updateVertices(){
+		updateVertices(vertices);
+	}
+
+	//For flagging an update with a full set of new data
 	public void updateVertices( FloatBuffer vertices ){
+		updateVertices(vertices, 0, vertices.limit());
+	}
+
+	//For flagging an update with a subset of data changed
+	public void updateVertices( FloatBuffer vertices, int start, int end){
 		this.vertices = vertices;
-		needsUpdate = true;
+
+		if (updateStart == -1)
+			updateStart = start;
+		else
+			updateStart = Math.min(start, updateStart);
+
+		if (updateEnd == -1)
+			updateEnd = end;
+		else
+			updateEnd = Math.max(end, updateEnd);
 	}
 
 	public void updateGLData(){
-		if (!needsUpdate) return;
+		if (updateStart == -1) return;
 
-		vertices.position(0);
+		vertices.position(updateStart);
 		bind();
-		GLES20.glBufferData(GLES20.GL_ARRAY_BUFFER, (vertices.limit()*4), vertices, GLES20.GL_DYNAMIC_DRAW);
+
+		if (updateStart == 0 && updateEnd == vertices.limit()){
+			GLES20.glBufferData(GLES20.GL_ARRAY_BUFFER, vertices.limit()*4, vertices, GLES20.GL_DYNAMIC_DRAW);
+		} else {
+			GLES20.glBufferSubData(GLES20.GL_ARRAY_BUFFER, updateStart*4, (updateEnd - updateStart)*4, vertices);
+		}
+
 		release();
-		needsUpdate = false;
+		updateStart = updateEnd = -1;
 	}
 
 	public void bind(){
@@ -77,7 +102,7 @@ public class Vertexbuffer {
 
 	public static void refreshAllBuffers(){
 		for (Vertexbuffer buf : buffers) {
-			buf.needsUpdate = true;
+			buf.updateVertices();
 			buf.updateGLData();
 		}
 	}