Refactor the "File → Export Image" command.

The existing code is horrible and needlessly platform-dependent.
Even worse, it causes a freeze on GTK. Instead of propping that up
with a few more crutches, just fix the root cause.

src/CMakeLists.txt

@@ -154,6 +154,7 @@ set(solvespace_core_SOURCES
     drawconstraint.cpp
     drawentity.cpp
     entity.cpp
+    export.cpp
     exportstep.cpp
     exportvector.cpp
     expr.cpp
@@ -191,7 +192,6 @@ set(solvespace_core_SOURCES
     srf/triangulate.cpp)
 
 set(solvespace_core_gl_SOURCES
-    export.cpp
     solvespace.cpp)
 
 add_library(solvespace-core STATIC

src/draw.cpp

@@ -885,14 +885,23 @@ void GraphicsWindow::Paint() {
                           /*outlineColor=*/Style::Color(Style::HOVERED));
     }
 
+    // If we've had a screenshot requested, take it now, before the UI is overlaid.
+    if(!SS.screenshotFile.empty()) {
+        FILE *f = ssfopen(SS.screenshotFile, "wb");
+        if(!f || !canvas->ReadFrame()->WritePng(f, /*flip=*/true)) {
+            Error("Couldn't write to '%s'", SS.screenshotFile.c_str());
+        }
+        if(f) fclose(f);
+        SS.screenshotFile.clear();
+    }
+
     // And finally the toolbar.
     if(SS.showToolbar) {
         canvas->SetCamera(camera);
         ToolbarDraw(&uiCanvas);
     }
 
-    // If we display UI elements, also display an fps counter.
-    if(SS.showToolbar) {
+    // Also display an fps counter.
     RgbaColor renderTimeColor;
     if(1000 / renderTime.count() < 60) {
         // We aim for a steady 60fps; draw the counter in red when we're slower.
@@ -904,7 +913,6 @@ void GraphicsWindow::Paint() {
                                      (long)renderTime.count(),
                                      (long)(1000/renderTime.count())),
                             5, 5, renderTimeColor);
-    }
 
     canvas->FlushFrame();
     canvas->Clear();

src/export.cpp

@@ -1117,39 +1117,8 @@ void SolveSpaceUI::ExportMeshAsThreeJsTo(FILE *f, const std::string &filename,
 // rendering the view in the usual way and then copying the pixels.
 //-----------------------------------------------------------------------------
 void SolveSpaceUI::ExportAsPngTo(const std::string &filename) {
-#if !defined(HEADLESS)
-    // No guarantee that the back buffer contains anything valid right now,
-    // so repaint the scene. And hide the toolbar too.
-    bool prevShowToolbar = SS.showToolbar;
-    SS.showToolbar = false;
-
-    // Somewhat hacky way to invoke glReadPixels without dragging in all OpenGL headers.
-    std::shared_ptr<ViewportCanvas> canvas = CreateRenderer();
-    canvas->SetCamera(SS.GW.GetCamera());
-    std::shared_ptr<Pixmap> screenshot;
-#if !defined(WIN32)
-    GlOffscreen offscreen;
-    offscreen.Render((int)SS.GW.width, (int)SS.GW.height, [&] {
+    screenshotFile = filename;
+    // The rest of the work is done in the next redraw.
     SS.GW.Paint();
-        screenshot = canvas->ReadFrame();
-    });
-#else
-    SS.GW.Paint();
-    screenshot = canvas->ReadFrame();
-#endif
-    SS.showToolbar = prevShowToolbar;
-
-    FILE *f = ssfopen(filename, "wb");
-    if(!f || !screenshot->WritePng(f, /*flip=*/true)) {
-        Error("Couldn't write to '%s'", filename.c_str());
-    }
-    if(f) fclose(f);
-
-#if !defined(WIN32)
-    offscreen.Clear();
-#endif
-
-    return;
-#endif
 }
 

src/solvespace.h

@@ -676,6 +676,7 @@ public:
     bool     drawBackFaces;
     bool     checkClosedContour;
     bool     showToolbar;
+    std::string screenshotFile;
     RgbaColor backgroundColor;
     bool     exportShadedTriangles;
     bool     exportPwlCurves;