Show memory report in debug builds (#187)

* Show memory report in debug builds

log::debug!() after wgpuSwapChainPresent(); assumed to be called roughly once
per frame; useful for detecting memory leaks

* wgpuGetResourceUsageString()

Returns resource usage as C string

ffi/wgpu.h

@@ -70,6 +70,9 @@ void wgpuSetLogLevel(WGPULogLevel level);
 
 uint32_t wgpuGetVersion(void);
 
+// Returns resource usage C string; caller owns the string and must free() it
+char* wgpuGetResourceUsageString();
+
 void wgpuRenderPassEncoderSetPushConstants(WGPURenderPassEncoder encoder, WGPUShaderStageFlags stages, uint32_t offset, uint32_t sizeBytes, void* const data);
 
 void wgpuBufferDrop(WGPUBuffer buffer);

src/lib.rs

@@ -213,6 +213,14 @@ pub extern "C" fn wgpuCreateInstance(
     8 as native::WGPUInstance
 }
 
+#[no_mangle]
+pub extern "C" fn wgpuGetResourceUsageString() -> *const std::os::raw::c_char {
+    let c_string = CString::new(format!("{:?}", GLOBAL.generate_report())).unwrap();
+    let ptr = c_string.as_ptr();
+    std::mem::forget(c_string);
+    ptr
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn wgpuInstanceCreateSurface(
     _: native::WGPUInstance,