Bug 1652894 - allow SWGL contexts to have multiple strong references. r=jimb

Differential Revision: https://phabricator.services.mozilla.com/D86337

gfx/webrender_bindings/src/swgl_bindings.rs

@@ -21,6 +21,11 @@ pub extern "C" fn wr_swgl_create_context() -> *mut c_void {
     swgl::Context::create().into()
 }
 
+#[no_mangle]
+pub extern "C" fn wr_swgl_reference_context(ctx: *mut c_void) {
+    swgl::Context::from(ctx).reference();
+}
+
 #[no_mangle]
 pub extern "C" fn wr_swgl_destroy_context(ctx: *mut c_void) {
     swgl::Context::from(ctx).destroy();

gfx/wr/swgl/src/gl.cc

@@ -512,6 +512,8 @@ struct ObjectStore {
 };
 
 struct Context {
+  int32_t references = 1;
+
   ObjectStore<Query> queries;
   ObjectStore<Buffer> buffers;
   ObjectStore<Texture> textures;
@@ -4093,8 +4095,11 @@ void BlitFramebuffer(GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1,
 
 void Finish() {}
 
-void MakeCurrent(void* ctx_ptr) {
-  ctx = (Context*)ctx_ptr;
+void MakeCurrent(Context* c) {
+  if (ctx == c) {
+    return;
+  }
+  ctx = c;
   if (ctx) {
     setup_program(ctx->current_program);
     blend_key = ctx->blend ? ctx->blend_key : BLEND_KEY_NONE;
@@ -4104,16 +4109,28 @@ void MakeCurrent(void* ctx_ptr) {
   }
 }
 
-void* CreateContext() { return new Context; }
+Context* CreateContext() { return new Context; }
 
-void DestroyContext(void* ctx_ptr) {
-  if (!ctx_ptr) {
+void ReferenceContext(Context* c) {
+  if (!c) {
     return;
   }
-  if (ctx == ctx_ptr) {
+  ++c->references;
+}
+
+void DestroyContext(Context* c) {
+  if (!c) {
+    return;
+  }
+  assert(c->references > 0);
+  --c->references;
+  if (c->references > 0) {
+    return;
+  }
+  if (ctx == c) {
     MakeCurrent(nullptr);
   }
-  delete (Context*)ctx_ptr;
+  delete c;
 }
 
 typedef Texture LockedTexture;

gfx/wr/swgl/src/swgl_fns.rs

@@ -300,6 +300,7 @@ extern "C" {
         flip: GLboolean,
     );
     fn CreateContext() -> *mut c_void;
+    fn ReferenceContext(ctx: *mut c_void);
     fn DestroyContext(ctx: *mut c_void);
     fn MakeCurrent(ctx: *mut c_void);
 }
@@ -312,6 +313,12 @@ impl Context {
         Context(unsafe { CreateContext() })
     }
 
+    pub fn reference(&self) {
+        unsafe {
+            ReferenceContext(self.0);
+         }
+     }
+
     pub fn destroy(&self) {
         unsafe {
             DestroyContext(self.0);