Bug 1406494 - Add a WR_RESOURCE_PATH environment variable that lets you set a resource override path for webrender. r=kats

This allows easier testing of shader changes. If you point this environment
variable at your gfx/webrender/res/ directory, the shaders will be read from
that directory when Firefox is launched, so you can test shader changes just by
restarting Firefox and don't need to recompile.

MozReview-Commit-ID: 9Dt6MhErnGS

--HG--
extra : rebase_source : 3c8cb83f28a6b6b00fb4437a7fd7f04dd5511633

gfx/layers/wr/WebRenderBridgeParent.cpp

@@ -64,6 +64,15 @@ bool gfx_use_wrench()
   return gfxEnv::EnableWebRenderRecording();
 }
 
+const char* gfx_wr_resource_path_override()
+{
+  const char* resourcePath = PR_GetEnv("WR_RESOURCE_Path");
+  if (!resourcePath || resourcePath[0] == '\0') {
+    return nullptr;
+  }
+  return resourcePath;
+}
+
 void gfx_critical_note(const char* msg)
 {
   gfxCriticalNote << msg;

gfx/webrender_bindings/src/bindings.rs

@@ -1,4 +1,4 @@
-use std::ffi::CString;
+use std::ffi::{CStr, CString};
 use std::{mem, slice};
 use std::path::PathBuf;
 use std::ptr;
@@ -415,6 +415,7 @@ extern "C" {
     // be disabled in WebRenderBridgeParent::ProcessWebRenderCommands
     // by commenting out the path that adds an external image ID
     fn gfx_use_wrench() -> bool;
+    fn gfx_wr_resource_path_override() -> *const c_char;
     fn gfx_critical_note(msg: *const c_char);
 }
 
@@ -644,6 +645,17 @@ pub extern "C" fn wr_window_new(window_id: WrWindowId,
         blob_image_renderer: Some(Box::new(Moz2dImageRenderer::new(workers.clone()))),
         workers: Some(workers.clone()),
         enable_render_on_scroll: false,
+        resource_override_path: unsafe {
+            let override_charptr = gfx_wr_resource_path_override();
+            if override_charptr.is_null() {
+                None
+            } else {
+                match CStr::from_ptr(override_charptr).to_str() {
+                    Ok(override_str) => Some(PathBuf::from(override_str)),
+                    _ => None
+                }
+            }
+        },
         ..Default::default()
     };
 

gfx/webrender_bindings/webrender_ffi.h

@@ -21,6 +21,7 @@ bool is_in_main_thread();
 bool is_in_render_thread();
 bool is_glcontext_egl(void* glcontext_ptr);
 bool gfx_use_wrench();
+const char* gfx_wr_resource_path_override();
 void gfx_critical_note(const char* msg);
 void* get_proc_address_from_glcontext(void* glcontext_ptr, const char* procname);
 

gfx/webrender_bindings/webrender_ffi_generated.h

@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-/* Generated with cbindgen:0.1.23 */
+/* Generated with cbindgen:0.1.25 */
 
 /* DO NOT MODIFY THIS MANUALLY! This file was generated using cbindgen.
  * To generate this file:
@@ -763,6 +763,8 @@ extern void gfx_critical_note(const char *aMsg);
 
 extern bool gfx_use_wrench();
 
+extern const char *gfx_wr_resource_path_override();
+
 extern bool is_glcontext_egl(void *aGlcontextPtr);
 
 extern bool is_in_compositor_thread();