Improvements to JS display implementation

Fix red and green channels being swapped due to different assumptions
in channel ordering between DingusPPC and the JS side.

Add content hashing of the frame buffer so that we don't need to
blit to the JS side if the content hasn't changed. Uses xxHash3
since it has the best performance.

Updates mihaip/infinite-mac#219
Updates mihaip/infinite-mac#18

devices/video/display_js.cpp

@@ -2,12 +2,18 @@
 #include <loguru.hpp>
 #include <emscripten.h>
 
+// Use xxHash in inline mode to avoid having to include a separate .c file.
+#define XXH_STATIC_LINKING_ONLY
+#define XXH_INLINE_ALL
+#include <thirdparty/xxHash/xxhash.h>
+
 class Display::Impl
 {
 public:
-    std::unique_ptr<uint8_t[]> browser_framebuffer;
-    int browser_framebuffer_size;
-    int browser_framebuffer_pitch;
+    std::unique_ptr<uint8_t[]> framebuffer;
+    int framebuffer_size;
+    int framebuffer_pitch;
+    XXH64_hash_t last_update_hash;
 };
 
 Display::Display(): impl(std::make_unique<Impl>())
@@ -21,9 +27,10 @@ Display::~Display() {
 
 bool Display::configure(int width, int height)
 {
-    impl->browser_framebuffer_pitch = width * 4;
-    impl->browser_framebuffer_size = height * impl->browser_framebuffer_pitch;
-    impl->browser_framebuffer = std::make_unique<uint8_t[]>(impl->browser_framebuffer_size);
+    impl->framebuffer_pitch = width * 4;
+    impl->framebuffer_size = height * impl->framebuffer_pitch;
+    impl->framebuffer = std::make_unique<uint8_t[]>(impl->framebuffer_size);
+    impl->last_update_hash = 0;
     EM_ASM_({ workerApi.didOpenVideo($0, $1); }, width, height);
     return true;
 }
@@ -36,22 +43,42 @@ void Display::handle_events(const WindowEvent& wnd_event)
 void Display::blank()
 {
     // Replace contents with opaque black.
-    uint8_t *browser_framebuffer = impl->browser_framebuffer.get();
-    int browser_framebuffer_size = impl->browser_framebuffer_size;
-    for (int i = 0; i < browser_framebuffer_size; i += 4) {
-        browser_framebuffer[i] = 0x00;
-        browser_framebuffer[i + 1] = 0x00;
-        browser_framebuffer[i + 2] = 0x00;
-        browser_framebuffer[i + 3] = 0xff;
+    uint8_t *framebuffer = impl->framebuffer.get();
+    int framebuffer_size = impl->framebuffer_size;
+    for (int i = 0; i < framebuffer_size; i += 4) {
+        framebuffer[i] = 0x00;
+        framebuffer[i + 1] = 0x00;
+        framebuffer[i + 2] = 0x00;
+        framebuffer[i + 3] = 0xff;
     }
-    EM_ASM_({ workerApi.blit($0, $1); }, browser_framebuffer, browser_framebuffer_size);
+    impl->last_update_hash = XXH3_64bits(framebuffer, framebuffer_size);
+    EM_ASM_({ workerApi.blit($0, $1); }, framebuffer, framebuffer_size);
 }
 
 void Display::update(std::function<void(uint8_t *dst_buf, int dst_pitch)> convert_fb_cb, bool draw_hw_cursor, int cursor_x, int cursor_y)
 {
-    convert_fb_cb(impl->browser_framebuffer.get(), impl->browser_framebuffer_pitch);
-    // TODO: has contents and avoid sending framebuffer if unchanged
-    EM_ASM_({ workerApi.blit($0, $1); }, impl->browser_framebuffer.get(), impl->browser_framebuffer_size);
+    uint8_t *framebuffer = impl->framebuffer.get();
+    size_t framebuffer_size = impl->framebuffer_size;
+    convert_fb_cb(framebuffer, impl->framebuffer_pitch);
+    // DingusPPC generates ARGB but in little endian order within a 32-bit word. s
+    // It ends up as BGRA in memory, so we need to swap red and blue channels
+    // to generate the RGBA that the JS side expects.
+    for (size_t i = 0; i < framebuffer_size; i += 4) {
+        std::swap(framebuffer[i], framebuffer[i + 2]);
+    }
+
+    XXH64_hash_t update_hash = XXH3_64bits(framebuffer, framebuffer_size);
+
+    if (update_hash == impl->last_update_hash) {
+        // Screen has not changed, but we still let the JS know so that it can
+        // keep track of screen refreshes when deciding how long to idle for.
+        EM_ASM({ workerApi.blit(0, 0); });
+        return;
+    }
+
+    impl->last_update_hash = update_hash;
+
+    EM_ASM_({ workerApi.blit($0, $1); }, framebuffer, framebuffer_size);
 }
 
 void Display::setup_hw_cursor(std::function<void(uint8_t *dst_buf, int dst_pitch)> draw_hw_cursor, int cursor_width, int cursor_height)

thirdparty/xxHash/README.md

@@ -0,0 +1,3 @@
+# xxHash
+
+Import of xxhash.h from https://github.com/Cyan4973/xxHash as of Cyan4973/xxHash@675eda553733666329e1052f8fd97ef599fdca63