Handle global mouse state for Emscripten (#12669)

Author: Temdog007

src/video/emscripten/SDL_emscriptenmouse.c

@@ -196,6 +196,26 @@ static bool Emscripten_SetRelativeMouseMode(bool enabled)
     return false;
 }
 
+static SDL_MouseButtonFlags Emscripten_GetGlobalMouseState(float *x, float *y)
+{
+    *x = MAIN_THREAD_EM_ASM_DOUBLE({
+        return Module['SDL3']['mouse_x'];
+    });
+    *y = MAIN_THREAD_EM_ASM_DOUBLE({
+        return Module['SDL3']['mouse_y'];
+    });
+    SDL_MouseButtonFlags flags = 0;
+    for (int i = 0; i < 5; ++i) {
+        const bool button_down = MAIN_THREAD_EM_ASM_INT({
+            return Module['SDL3']['mouse_buttons'][$0];
+        }, i);
+        if (button_down) {
+            flags |= 1 << i;
+        }
+    }
+    return flags;
+}
+
 void Emscripten_InitMouse(void)
 {
     SDL_Mouse *mouse = SDL_GetMouse();
@@ -206,6 +226,46 @@ void Emscripten_InitMouse(void)
     mouse->CreateSystemCursor = Emscripten_CreateSystemCursor;
     mouse->SetRelativeMouseMode = Emscripten_SetRelativeMouseMode;
 
+    // Add event listeners to track mouse events on the document
+    MAIN_THREAD_EM_ASM({
+        if (!Module['SDL3']) {
+            Module['SDL3'] = {};
+        }
+        var SDL3 = Module['SDL3'];
+        SDL3['mouse_x'] = 0;
+        SDL3['mouse_y'] = 0;
+        /*
+            Based on https://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/button
+            Possible value for button in the event object is [0, 5)
+            NOTE: Some browsers do not allow handling the forwards and backwards buttons
+        */
+        SDL3['mouse_buttons'] = [];
+        for (var i = 0; i < 5; ++i) {
+            SDL3['mouse_buttons'][i] = false;
+        }
+        document.addEventListener('mousemove', function(e) {
+            // Reacquire from object in case it changed for some reason
+            var SDL3 = Module['SDL3'];
+            SDL3['mouse_x'] = e.clientX;
+            SDL3['mouse_y'] = e.clientY;
+        });
+        document.addEventListener('mousedown', function(e) {
+            // Reacquire from object in case it changed for some reason
+            var SDL3 = Module['SDL3'];
+            if (0 <= e.button && e.button < SDL3['mouse_buttons'].length) {
+                SDL3['mouse_buttons'][e.button] = true;
+            }
+        });
+        document.addEventListener('mouseup', function(e) {
+            // Reacquire from object in case it changed for some reason
+            var SDL3 = Module['SDL3'];
+            if (0 <= e.button && e.button < SDL3['mouse_buttons'].length) {
+                SDL3['mouse_buttons'][e.button] = false;
+            }
+        });
+    });
+    mouse->GetGlobalMouseState = Emscripten_GetGlobalMouseState;
+
     SDL_SetDefaultCursor(Emscripten_CreateDefaultCursor());
 }
 

test/testmouse.c

@@ -117,6 +117,8 @@ static void loop(void *arg)
     struct mouse_loop_data *loop_data = (struct mouse_loop_data *)arg;
     SDL_Event event;
     SDL_Renderer *renderer = loop_data->renderer;
+    float fx, fy;
+    SDL_MouseButtonFlags flags;
 
     /* Check for events */
     while (SDL_PollEvent(&event)) {
@@ -265,6 +267,10 @@ static void loop(void *arg)
         DrawObject(renderer, active);
     }
 
+    flags = SDL_GetGlobalMouseState(&fx, &fy);
+    SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
+    SDL_RenderDebugTextFormat(renderer, 0, 0, "Global Mouse State: x=%f y=%f flags=%" SDL_PRIu32, fx, fy, flags);
+
     SDL_RenderPresent(renderer);
 
 #ifdef SDL_PLATFORM_EMSCRIPTEN