Address review comments

Set resolution in params for test scene. Add comments explaining division of work.

examples/scenes/src/test_scenes.rs

diff --git a/examples/scenes/src/test_scenes.rs b/examples/scenes/src/test_scenes.rs
index 2e36a39..e03792a 100644
--- a/examples/scenes/src/test_scenes.rs
+++ b/examples/scenes/src/test_scenes.rs
@@ -1523,11 +1523,12 @@
     ]
 }
 
-fn many_draw_objects(scene: &mut Scene, _: &mut SceneParams) {
+fn many_draw_objects(scene: &mut Scene, params: &mut SceneParams) {
     const N_WIDE: usize = 300;
     const N_HIGH: usize = 300;
     const SCENE_WIDTH: f64 = 2000.0;
     const SCENE_HEIGHT: f64 = 1500.0;
+    params.resolution = Some((SCENE_WIDTH, SCENE_HEIGHT).into());
     for j in 0..N_HIGH {
         let y = (j as f64 + 0.5) * (SCENE_HEIGHT / N_HIGH as f64);
         for i in 0..N_WIDE {

shader/draw_leaf.wgsl

diff --git a/shader/draw_leaf.wgsl b/shader/draw_leaf.wgsl
index e512661..e041a51 100644
--- a/shader/draw_leaf.wgsl
+++ b/shader/draw_leaf.wgsl
@@ -74,7 +74,8 @@
     workgroupBarrier();
     var prefix = sh_scratch[0];
 
-    let num_blocks_total = (config.n_drawobj + (WG_SIZE - 1u)) / WG_SIZE;
+    // This is the same division of work as draw_reduce.
+    let num_blocks_total = (config.n_drawobj + WG_SIZE - 1u) / WG_SIZE;
     let n_blocks_base = num_blocks_total / WG_SIZE;
     let remainder = num_blocks_total % WG_SIZE;
     let first_block = n_blocks_base * wg_id.x + min(wg_id.x, remainder);

shader/draw_reduce.wgsl

diff --git a/shader/draw_reduce.wgsl b/shader/draw_reduce.wgsl
index 4a7fb6d..7a12b81 100644
--- a/shader/draw_reduce.wgsl
+++ b/shader/draw_reduce.wgsl
@@ -25,6 +25,9 @@
     @builtin(workgroup_id) wg_id: vec3<u32>,
 ) {
     let num_blocks_total = (config.n_drawobj + (WG_SIZE - 1u)) / WG_SIZE;
+    // When the number of blocks exceeds the workgroup size, divide
+    // the work evenly so each workgroup handles n_blocks / wg, with
+    // the low workgroups doing one more each to handle the remainder.
     let n_blocks_base = num_blocks_total / WG_SIZE;
     let remainder = num_blocks_total % WG_SIZE;
     let first_block = n_blocks_base * wg_id.x + min(wg_id.x, remainder);