Fix skipped depth bias set on Metal (#6276)

filament/backend/src/metal/MetalContext.h

@@ -96,6 +96,8 @@ struct MetalContext {
     SamplerStateCache samplerStateCache;
     ArgumentEncoderCache argumentEncoderCache;
 
+    PolygonOffset currentPolygonOffset = {0.0f, 0.0f};
+
     MetalSamplerGroup* samplerBindings[Program::SAMPLER_BINDING_COUNT] = {};
 
     // Keeps track of sampler groups we've finalized for the current render pass.

filament/backend/src/metal/MetalDriver.mm

@@ -1005,6 +1005,7 @@ void MetalDriver::beginRenderPass(Handle<HwRenderTarget> rth,
     mContext->depthStencilState.invalidate();
     mContext->cullModeState.invalidate();
     mContext->windingState.invalidate();
+    mContext->currentPolygonOffset = {0.0f, 0.0f};
 
     mContext->finalizedSamplerGroups.clear();
 }
@@ -1590,10 +1591,12 @@ void MetalDriver::draw(PipelineState ps, Handle<HwRenderPrimitive> rph, uint32_t
         [mContext->currentRenderPassEncoder setDepthStencilState:state];
     }
 
-    if (ps.polygonOffset.constant != 0.0 || ps.polygonOffset.slope != 0.0) {
+    if (ps.polygonOffset.constant != mContext->currentPolygonOffset.constant ||
+        ps.polygonOffset.slope != mContext->currentPolygonOffset.slope) {
         [mContext->currentRenderPassEncoder setDepthBias:ps.polygonOffset.constant
                                               slopeScale:ps.polygonOffset.slope
                                                    clamp:0.0];
+        mContext->currentPolygonOffset = ps.polygonOffset;
     }
 
     // Set scissor-rectangle.