Examples: SDL: Using SDL_CaptureMouse() to retrieve coordinates outside of client area when dragging. (#1559)

Digging into sdl window/mouse stuff will also be useful for multi-viewport work.

examples/sdl_opengl2_example/imgui_impl_sdl_gl2.cpp

@@ -270,23 +270,33 @@ void ImGui_ImplSdlGL2_NewFrame(SDL_Window *window)
     io.DeltaTime = g_Time > 0.0 ? (float)(current_time - g_Time) : (float)(1.0f / 60.0f);
     g_Time = current_time;
 
-    // Setup inputs
-    // (we already got mouse wheel, keyboard keys & characters from SDL_PollEvent())
+    // Setup mouse inputs (we already got mouse wheel, keyboard keys & characters from our event handler)
     int mx, my;
     Uint32 mouse_buttons = SDL_GetMouseState(&mx, &my);
-    if (SDL_GetWindowFlags(window) & SDL_WINDOW_INPUT_FOCUS)
-        io.MousePos = ImVec2((float)mx, (float)my);
-    else
-        io.MousePos = ImVec2(-FLT_MAX,-FLT_MAX);
-
+    io.MousePos = ImVec2(-FLT_MAX, -FLT_MAX);
+    io.MouseWheel = g_MouseWheel;
     io.MouseDown[0] = g_MousePressed[0] || (mouse_buttons & SDL_BUTTON(SDL_BUTTON_LEFT)) != 0;  // If a mouse press event came, always pass it as "mouse held this frame", so we don't miss click-release events that are shorter than 1 frame.
     io.MouseDown[1] = g_MousePressed[1] || (mouse_buttons & SDL_BUTTON(SDL_BUTTON_RIGHT)) != 0;
     io.MouseDown[2] = g_MousePressed[2] || (mouse_buttons & SDL_BUTTON(SDL_BUTTON_MIDDLE)) != 0;
     g_MousePressed[0] = g_MousePressed[1] = g_MousePressed[2] = false;
-
-    io.MouseWheel = g_MouseWheel;
     g_MouseWheel = 0.0f;
 
+    // We need to use SDL_CaptureMouse() to easily retrieve mouse coordinates outside of the client area. This is only supported from SDL 2.0.4 (released Jan 2016)
+#if (SDL_MAJOR_VERSION >= 2) && (SDL_MINOR_VERSION >= 0) && (SDL_PATCHLEVEL >= 4)   
+    if ((SDL_GetWindowFlags(window) & (SDL_WINDOW_MOUSE_FOCUS | SDL_WINDOW_MOUSE_CAPTURE)) != 0)
+        io.MousePos = ImVec2((float)mx, (float)my);
+    bool any_mouse_button_down = false;
+    for (int n = 0; n < IM_ARRAYSIZE(io.MouseDown); n++)
+        any_mouse_button_down |= io.MouseDown[n];
+    if (any_mouse_button_down && (SDL_GetWindowFlags(window) & SDL_WINDOW_MOUSE_CAPTURE) == 0)
+        SDL_CaptureMouse(SDL_TRUE);
+    if (!any_mouse_button_down && (SDL_GetWindowFlags(window) & SDL_WINDOW_MOUSE_CAPTURE) != 0)
+        SDL_CaptureMouse(SDL_FALSE);
+#else
+    if ((SDL_GetWindowFlags(window) & SDL_WINDOW_INPUT_FOCUS) != 0)
+        io.MousePos = ImVec2((float)mx, (float)my);
+#endif
+
     // Hide OS mouse cursor if ImGui is drawing it
     SDL_ShowCursor(io.MouseDrawCursor ? 0 : 1);
 

examples/sdl_opengl3_example/imgui_impl_sdl_gl3.cpp

@@ -381,23 +381,33 @@ void ImGui_ImplSdlGL3_NewFrame(SDL_Window* window)
     io.DeltaTime = g_Time > 0.0 ? (float)(current_time - g_Time) : (float)(1.0f / 60.0f);
     g_Time = current_time;
 
-    // Setup inputs
-    // (we already got mouse wheel, keyboard keys & characters from SDL_PollEvent())
+    // Setup mouse inputs (we already got mouse wheel, keyboard keys & characters from our event handler)
     int mx, my;
     Uint32 mouse_buttons = SDL_GetMouseState(&mx, &my);
-    if (SDL_GetWindowFlags(window) & SDL_WINDOW_INPUT_FOCUS)
-        io.MousePos = ImVec2((float)mx, (float)my);
-    else
-        io.MousePos = ImVec2(-FLT_MAX, -FLT_MAX);
-
-    io.MouseDown[0] = g_MousePressed[0] || (mouse_buttons & SDL_BUTTON(SDL_BUTTON_LEFT)) != 0; // If a mouse press event came, always pass it as "mouse held this frame", so we don't miss click-release events that are shorter than 1 frame.
+    io.MousePos = ImVec2(-FLT_MAX, -FLT_MAX);
+    io.MouseWheel = g_MouseWheel;
+    io.MouseDown[0] = g_MousePressed[0] || (mouse_buttons & SDL_BUTTON(SDL_BUTTON_LEFT)) != 0;  // If a mouse press event came, always pass it as "mouse held this frame", so we don't miss click-release events that are shorter than 1 frame.
     io.MouseDown[1] = g_MousePressed[1] || (mouse_buttons & SDL_BUTTON(SDL_BUTTON_RIGHT)) != 0;
     io.MouseDown[2] = g_MousePressed[2] || (mouse_buttons & SDL_BUTTON(SDL_BUTTON_MIDDLE)) != 0;
     g_MousePressed[0] = g_MousePressed[1] = g_MousePressed[2] = false;
-
-    io.MouseWheel = g_MouseWheel;
     g_MouseWheel = 0.0f;
 
+    // We need to use SDL_CaptureMouse() to easily retrieve mouse coordinates outside of the client area. This is only supported from SDL 2.0.4 (released Jan 2016)
+#if (SDL_MAJOR_VERSION >= 2) && (SDL_MINOR_VERSION >= 0) && (SDL_PATCHLEVEL >= 4)   
+    if ((SDL_GetWindowFlags(window) & (SDL_WINDOW_MOUSE_FOCUS | SDL_WINDOW_MOUSE_CAPTURE)) != 0)
+        io.MousePos = ImVec2((float)mx, (float)my);
+    bool any_mouse_button_down = false;
+    for (int n = 0; n < IM_ARRAYSIZE(io.MouseDown); n++)
+        any_mouse_button_down |= io.MouseDown[n];
+    if (any_mouse_button_down && (SDL_GetWindowFlags(window) & SDL_WINDOW_MOUSE_CAPTURE) == 0)
+        SDL_CaptureMouse(SDL_TRUE);
+    if (!any_mouse_button_down && (SDL_GetWindowFlags(window) & SDL_WINDOW_MOUSE_CAPTURE) != 0)
+        SDL_CaptureMouse(SDL_FALSE);
+#else
+    if ((SDL_GetWindowFlags(window) & SDL_WINDOW_INPUT_FOCUS) != 0)
+        io.MousePos = ImVec2((float)mx, (float)my);
+#endif
+
     // Hide OS mouse cursor if ImGui is drawing it
     SDL_ShowCursor(io.MouseDrawCursor ? 0 : 1);