Fix high DPI rendering on MacOS

According to the SDL2 docs, `SDL_GetWindowSize` returns the client
window size in screen coordinates, `SDL_GL_GetDrawableSize` returns the
size in pixels.

This change makes sure the `glViewport` calls always use pixels.

Author: binji

src/host-ui-imgui.cc

@@ -288,7 +288,8 @@ void HostUI::begin_frame() {
 
 void HostUI::end_frame() {
   ImGuiIO& io = ImGui::GetIO();
-  glViewport(0, 0, io.DisplaySize.x, io.DisplaySize.y);
+  glViewport(0, 0, io.DisplaySize.x * io.DisplayFramebufferScale.x,
+             io.DisplaySize.y * io.DisplayFramebufferScale.y);
   glClearColor(0.1f, 0.1f, 0.1f, 1);
   glClear(GL_COLOR_BUFFER_BIT);
   ImGui::Render();

src/host-ui-simple.c

@@ -104,7 +104,7 @@ void host_ui_event(struct HostUI* ui, union SDL_Event* event) {
       (event->window.event == SDL_WINDOWEVENT_SHOWN ||
        event->window.event == SDL_WINDOWEVENT_RESIZED)) {
     int iw, ih;
-    SDL_GetWindowSize(ui->window, &iw, &ih);
+    SDL_GL_GetDrawableSize(ui->window, &iw, &ih);
     f32 w = iw, h = ih;
     f32 aspect = w / h;
     f32 want_aspect = (f32)SCREEN_WIDTH / SCREEN_HEIGHT;