Add an interface for view-independent rendering.

To actually achieve improved performance with the OpenGL 2 renderer,
we have to cache geometry that doesn't change when the viewport does
(note that the rendered pixels can change quite dramatically because
we can reconfigure shaders; e.g. stippling can be drawn in screen
coordinates).

This commit adds a BatchCanvas interface that can be implemented
by renderers, and uses it for drawing entities such as lines and
points.

src/confscreen.cpp

@@ -80,6 +80,7 @@ void TextWindow::ScreenChangeFixExportColors(int link, uint32_t v) {
 
 void TextWindow::ScreenChangeBackFaces(int link, uint32_t v) {
     SS.drawBackFaces = !SS.drawBackFaces;
+    SS.GW.persistentDirty = true;
     InvalidateGraphics();
 }
 

src/draw.cpp

@@ -562,12 +562,9 @@ void GraphicsWindow::DrawSnapGrid(Canvas *canvas) {
     }
 }
 
-void GraphicsWindow::DrawPersistent(Canvas *canvas) {
-    // Draw the active group; this does stuff like the mesh and edges.
-    SK.GetGroup(activeGroup)->Draw(canvas);
-
-    // Now draw the entities.
+void GraphicsWindow::DrawEntities(Canvas *canvas, bool persistent) {
     for(Entity &e : SK.entity) {
+        if(persistent == (e.IsNormal() || e.IsWorkplane())) continue;
         switch(SS.GW.drawOccludedAs) {
             case DrawOccludedAs::VISIBLE:
                 e.Draw(Entity::DrawAs::OVERLAY, canvas);
@@ -581,6 +578,14 @@ void GraphicsWindow::DrawPersistent(Canvas *canvas) {
                 break;
         }
     }
+}
+
+void GraphicsWindow::DrawPersistent(Canvas *canvas) {
+    // Draw the active group; this does stuff like the mesh and edges.
+    SK.GetGroup(activeGroup)->Draw(canvas);
+
+    // Now draw the entities that don't change with viewport.
+    DrawEntities(canvas, /*persistent=*/true);
 
     // Draw filled paths in all groups, when those filled paths were requested
     // specially by assigning a style with a fill color, or when the filled
@@ -629,7 +634,22 @@ void GraphicsWindow::Draw(Canvas *canvas) {
     if(showSnapGrid) DrawSnapGrid(canvas);
 
     // Draw all the things that don't change when we rotate.
-    DrawPersistent(canvas);
+    if(persistentCanvas != NULL) {
+        if(persistentDirty) {
+            persistentDirty = false;
+
+            persistentCanvas->Clear();
+            DrawPersistent(&*persistentCanvas);
+            persistentCanvas->Finalize();
+        }
+
+        persistentCanvas->Draw();
+    } else {
+        DrawPersistent(canvas);
+    }
+
+    // Draw the entities that do change with viewport.
+    DrawEntities(canvas, /*persistent=*/false);
 
     // Draw the polygon errors.
     if(SS.checkClosedContour) {

src/generate.cpp

@@ -352,6 +352,8 @@ void SolveSpaceUI::GenerateAll(Generate type, bool andFindFree, bool genForBBox)
 
     FreeAllTemporary();
     allConsistent = true;
+    SS.GW.persistentDirty = true;
+
     endMillis = GetMilliseconds();
 
     if(endMillis - startMillis > 30) {

src/graphicswin.cpp

@@ -206,6 +206,10 @@ std::string SolveSpace::MakeAcceleratorLabel(int accel) {
 
 void GraphicsWindow::Init() {
     canvas = CreateRenderer();
+    if(canvas) {
+        persistentCanvas = canvas->CreateBatch();
+        persistentDirty = true;
+    }
 
     scale = 5;
     offset    = Vector::From(0, 0, 0);

src/render/render.cpp

@@ -211,6 +211,18 @@ Canvas::hFill Canvas::GetFill(const Fill &fill) {
     return fills.AddAndAssignId(&fillCopy);
 }
 
+std::shared_ptr<BatchCanvas> Canvas::CreateBatch() {
+    return std::shared_ptr<BatchCanvas>();
+}
+
+//-----------------------------------------------------------------------------
+// An interface for view-independent visualization
+//-----------------------------------------------------------------------------
+
+const Camera &BatchCanvas::GetCamera() const {
+    ssassert(false, "Geometry drawn on BatchCanvas must be independent from camera");
+}
+
 //-----------------------------------------------------------------------------
 // A wrapper around Canvas that simplifies drawing UI in screen coordinates
 //-----------------------------------------------------------------------------

src/render/render.h

@@ -50,6 +50,8 @@ public:
     Vector      lightDirection[2];
 };
 
+class BatchCanvas;
+
 // An interface for populating a drawing area with geometry.
 class Canvas {
 public:
@@ -162,9 +164,11 @@ public:
                             const Vector &o, const Vector &u, const Vector &v,
                             const Point2d &ta, const Point2d &tb, hFill hcf) = 0;
     virtual void InvalidatePixmap(std::shared_ptr<const Pixmap> pm) = 0;
+
+    virtual std::shared_ptr<BatchCanvas> CreateBatch();
 };
 
-// An interface for view-dependent visualization
+// An interface for view-dependent visualization.
 class ViewportCanvas : public Canvas {
 public:
     virtual void SetCamera(const Camera &camera, bool filp = FLIP_FRAMEBUFFER) = 0;
@@ -177,6 +181,15 @@ public:
     virtual void GetIdent(const char **vendor, const char **renderer, const char **version) = 0;
 };
 
+// An interface for view-independent visualization.
+class BatchCanvas : public Canvas {
+public:
+    const Camera &GetCamera() const override;
+
+    virtual void Finalize() = 0;
+    virtual void Draw() = 0;
+};
+
 // A wrapper around Canvas that simplifies drawing UI in screen coordinates.
 class UiCanvas {
 public:

src/style.cpp

@@ -491,6 +491,7 @@ void TextWindow::ScreenChangeStylePatternType(int link, uint32_t v) {
     hStyle hs = { v };
     Style *s = Style::Get(hs);
     s->stippleType = (StipplePattern)(link - 1);
+    SS.GW.persistentDirty = true;
 }
 
 void TextWindow::ScreenChangeStyleMetric(int link, uint32_t v) {
@@ -639,6 +640,7 @@ void TextWindow::ScreenChangeStyleYesNo(int link, uint32_t v) {
             s->textOrigin = (Style::TextOrigin)((uint32_t)s->textOrigin |  (uint32_t)Style::TextOrigin::TOP);
             break;
     }
+    SS.GW.persistentDirty = true;
     InvalidateGraphics();
 }
 
@@ -721,6 +723,7 @@ bool TextWindow::EditControlDoneForStyles(const char *str) {
         }
         default: return false;
     }
+    SS.GW.persistentDirty = true;
     return true;
 }
 

src/textscreens.cpp

@@ -61,6 +61,7 @@ void TextWindow::ScreenShowGroupsSpecial(int link, uint32_t v) {
         Group *g = SK.GetGroup(SK.groupOrder.elem[i]);
         g->visible = state;
     }
+    SS.GW.persistentDirty = true;
 }
 void TextWindow::ScreenActivateGroup(int link, uint32_t v) {
     SS.GW.activeGroup.v = v;

src/ui.h

@@ -501,6 +501,8 @@ public:
     static void MenuClipboard(Command id);
 
     std::shared_ptr<ViewportCanvas> canvas;
+    std::shared_ptr<BatchCanvas>    persistentCanvas;
+    bool persistentDirty;
 
     // The width and height (in pixels) of the window.
     double width, height;
@@ -738,6 +740,7 @@ public:
     void UpdateDraggedNum(Vector *pos, double mx, double my);
     void UpdateDraggedPoint(hEntity hp, double mx, double my);
 
+    void DrawEntities(Canvas *canvas, bool persistent);
     void DrawPersistent(Canvas *canvas);
     void Draw(Canvas *canvas);