Readback depth from GPU picking (#1752)

* gpu picking in the viewer picks up depth now
* WebGL workarounds

crates/re_renderer/examples/picking.rs

@@ -102,19 +102,19 @@ impl framework::Example for Picking {
             PickingLayerProcessor::next_readback_result::<()>(re_ctx, READBACK_IDENTIFIER)
         {
             // Grab the middle pixel. usually we'd want to do something clever that snaps the the closest object of interest.
-            let picked_pixel = picking_result.picking_data[(picking_result.rect.extent.x / 2
-                + (picking_result.rect.extent.y / 2) * picking_result.rect.extent.x)
-                as usize];
+            let picked_id = picking_result.picked_id(picking_result.rect.extent / 2);
+            //let picked_position =
+            //    picking_result.picked_world_position(picking_result.rect.extent / 2);
+            //dbg!(picked_position, picked_id);
 
             self.mesh_is_hovered = false;
-            if picked_pixel == MESH_ID {
+            if picked_id == MESH_ID {
                 self.mesh_is_hovered = true;
-            } else if picked_pixel.object.0 != 0
-                && picked_pixel.object.0 <= self.point_sets.len() as u64
+            } else if picked_id.object.0 != 0 && picked_id.object.0 <= self.point_sets.len() as u64
             {
-                let point_set = &mut self.point_sets[picked_pixel.object.0 as usize - 1];
-                point_set.radii[picked_pixel.instance.0 as usize] = Size::new_scene(0.1);
-                point_set.colors[picked_pixel.instance.0 as usize] = Color32::DEBUG_COLOR;
+                let point_set = &mut self.point_sets[picked_id.object.0 as usize - 1];
+                point_set.radii[picked_id.instance.0 as usize] = Size::new_scene(0.1);
+                point_set.colors[picked_id.instance.0 as usize] = Color32::DEBUG_COLOR;
             }
         }
 

crates/re_renderer/shader/copy_texture.wgsl

@@ -0,0 +1,15 @@
+// Reads the content of a texture and writes it out as is.
+//
+// This is needed e.g. on WebGL to convert from a depth format to a regular color format that can be read back to the CPU.
+
+#import <./types.wgsl>
+#import <./global_bindings.wgsl>
+#import <./screen_triangle_vertex.wgsl>
+
+@group(1) @binding(0)
+var tex: texture_2d<f32>;
+
+@fragment
+fn main(in: FragmentInput) -> @location(0) Vec4 {
+    return textureSample(tex, nearest_sampler, in.texcoord);
+}

crates/re_renderer/src/allocator/gpu_readback_belt.rs

@@ -86,7 +86,8 @@ impl GpuReadbackBuffer {
                 },
             );
 
-            self.range_in_chunk = start_offset..self.range_in_chunk.end;
+            self.range_in_chunk =
+                (start_offset + buffer_info.buffer_size_padded)..self.range_in_chunk.end;
         }
     }
 

crates/re_renderer/src/config.rs

@@ -5,7 +5,7 @@
 #[derive(Clone, Copy, Debug)]
 pub enum HardwareTier {
     /// For WebGL and native OpenGL. Maintains strict WebGL capability.
-    Basic,
+    Web,
 
     /// Run natively with Vulkan/Metal but don't demand anything that isn't widely available.
     Native,
@@ -17,7 +17,15 @@ impl HardwareTier {
     /// Whether the current hardware tier supports sampling from textures with a sample count higher than 1.
     pub fn support_sampling_msaa_texture(&self) -> bool {
         match self {
-            HardwareTier::Basic => false,
+            HardwareTier::Web => false,
+            HardwareTier::Native => true,
+        }
+    }
+
+    /// Whether the current hardware tier supports sampling from textures with a sample count higher than 1.
+    pub fn support_depth_readback(&self) -> bool {
+        match self {
+            HardwareTier::Web => false,
             HardwareTier::Native => true,
         }
     }
@@ -27,7 +35,7 @@ impl Default for HardwareTier {
     fn default() -> Self {
         // Use "Basic" tier for actual web but also if someone forces the GL backend!
         if supported_backends() == wgpu::Backends::GL {
-            HardwareTier::Basic
+            HardwareTier::Web
         } else {
             HardwareTier::Native
         }
@@ -63,7 +71,11 @@ impl HardwareTier {
     /// Downlevel features required by the given tier.
     pub fn required_downlevel_capabilities(self) -> wgpu::DownlevelCapabilities {
         wgpu::DownlevelCapabilities {
-            flags: wgpu::DownlevelFlags::empty(),
+            flags: match self {
+                HardwareTier::Web => wgpu::DownlevelFlags::empty(),
+                // Require fully WebGPU compliance for the native tier.
+                HardwareTier::Native => wgpu::DownlevelFlags::all(),
+            },
             limits: Default::default(), // unused so far both here and in wgpu
             shader_model: wgpu::ShaderModel::Sm4,
         }