diff --git a/client/index.js b/client/index.js
index 7efa149..be8101f 100644
--- a/client/index.js
+++ b/client/index.js
@@ -173,7 +173,7 @@ function main() {
         },
 
         'players': {},
-        'onscreen_segments': [],
+        'onscreen_segments': null,
     };
 
     const context = {
diff --git a/client/math.js b/client/math.js
index 39c7d7a..73d31c8 100644
--- a/client/math.js
+++ b/client/math.js
@@ -217,8 +217,20 @@ function quad_fully_onscreen(screen, bbox) {
 
 function segments_onscreen(state, context) {
     // TODO: handle stroke width
+    
+    if (state.onscreen_segments === null) {       
+        let total_points = 0;
 
-    state.onscreen_segments.length = 0;
+        for (const event of state.events) {
+            if (event.type === EVENT.STROKE && !event.deleted) {
+                total_points += event.points.length - 1;
+            }
+        }
+
+        state.onscreen_segments = new Uint32Array(total_points * 6);
+    }
+
+    let at = 0;
 
     const screen_topleft = screen_to_canvas(state, {'x': 0, 'y': 0});
     const screen_bottomright = screen_to_canvas(state, {'x': context.canvas.width, 'y': context.canvas.height});
@@ -240,12 +252,20 @@ function segments_onscreen(state, context) {
                     if (fully_onscreen || segment_interesects_quad(a, b, screen_topleft, screen_bottomright, screen_topright, screen_bottomleft)) {
                         let base = head + j * 4;
                         // We draw quads as [1, 2, 3, 4, 3, 2]
-                        state.onscreen_segments.push(base + 0, base + 1, base + 2);
-                        state.onscreen_segments.push(base + 3, base + 2, base + 1);
+                        state.onscreen_segments[at + 0] = base + 0;
+                        state.onscreen_segments[at + 1] = base + 1;
+                        state.onscreen_segments[at + 2] = base + 2;
+                        state.onscreen_segments[at + 3] = base + 3;
+                        state.onscreen_segments[at + 4] = base + 2;
+                        state.onscreen_segments[at + 5] = base + 1;
+
+                        at += 6;
                     }
                 }
             }
             head += (event.points.length - 1) * 4;
         }
     }
+
+    return at;
 }
diff --git a/client/webgl_draw.js b/client/webgl_draw.js
index ef87a4c..7703e50 100644
--- a/client/webgl_draw.js
+++ b/client/webgl_draw.js
@@ -69,16 +69,16 @@ function draw(state, context) {
         }
 
         const before_clip = performance.now();
-        segments_onscreen(state, context); 
+        const index_count = segments_onscreen(state, context); 
         const after_clip = performance.now();
         console.debug('clip', after_clip - before_clip);
 
         gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, buffers['b_packed_static_index']);
-        gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint32Array(state.onscreen_segments), gl.DYNAMIC_DRAW);
+        gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint32Array(state.onscreen_segments.buffer, 0, index_count), gl.DYNAMIC_DRAW);
         const after_index_uploads = performance.now();
-        console.debug('index upload', after_index_uploads - after_clip);
+        // console.debug('index upload', after_index_uploads - after_clip);
 
-        gl.drawElements(gl.TRIANGLES, state.onscreen_segments.length, gl.UNSIGNED_INT, 0);
+        gl.drawElements(gl.TRIANGLES, index_count, gl.UNSIGNED_INT, 0);
     }
 
     if (dynamic_points > 0) {