From 48ba111cccdf93fedbb341cb5a8602e88a4812af Mon Sep 17 00:00:00 2001
From: Ben Doherty <bendoherty@google.com>
Date: Mon, 10 Feb 2020 10:34:44 -0800
Subject: [PATCH] Fix crash in Metal backend with screen-space refractions
 (#2104)

---
 filament/backend/src/metal/MetalDriver.mm  | 3 +++
 filament/backend/src/metal/MetalHandles.mm | 6 ++++++
 2 files changed, 9 insertions(+)

diff --git a/filament/backend/src/metal/MetalDriver.mm b/filament/backend/src/metal/MetalDriver.mm
index dc7ab1b757..9705d7d433 100644
--- a/filament/backend/src/metal/MetalDriver.mm
+++ b/filament/backend/src/metal/MetalDriver.mm
@@ -850,6 +850,9 @@ void MetalDriver::blit(TargetBufferFlags buffers,
     id<MTLTexture> srcTexture = srcTarget->getBlitColorSource();
     id<MTLTexture> dstTexture = dstTarget->getColor();
 
+    ASSERT_PRECONDITION(srcTexture != nil && dstTexture != nil,
+            "Source texture and destination texture must not be nil");
+
     // Metal's texture coordinates have (0, 0) at the top-left of the texture, but Filament's
     // coordinates have (0, 0) at bottom-left.
     MTLRegion srcRegion = MTLRegionMake2D(
diff --git a/filament/backend/src/metal/MetalHandles.mm b/filament/backend/src/metal/MetalHandles.mm
index e64bd0ad87..31b452dffa 100644
--- a/filament/backend/src/metal/MetalHandles.mm
+++ b/filament/backend/src/metal/MetalHandles.mm
@@ -441,6 +441,9 @@ id<MTLTexture> MetalRenderTarget::getDepthResolve() {
 }
 
 id<MTLTexture> MetalRenderTarget::getBlitColorSource() {
+    if (defaultRenderTarget) {
+        return acquireDrawable(context);
+    }
     if (color) {
         return color;
     }
@@ -448,6 +451,9 @@ id<MTLTexture> MetalRenderTarget::getBlitColorSource() {
 }
 
 id<MTLTexture> MetalRenderTarget::getBlitDepthSource() {
+    if (defaultRenderTarget) {
+        return acquireDepthTexture(context);
+    }
     if (depth) {
         return depth;
     }