cut the GPU load of moving the mouse over the 3D viewport (#15674)

Co-authored-by: Rodrigo Faselli <162915171+RF47@users.noreply.github.com>

src/slic3r/GUI/SceneCache.hpp

@@ -0,0 +1,56 @@
+#pragma once
+
+#include "libslic3r/Point.hpp"
+
+#include <array>
+#include <vector>
+
+namespace Slic3r {
+namespace GUI {
+
+class GLModel;
+
+// The last 3D scene pass, kept as a texture for frames that only rebuild the overlay.
+class SceneCache
+{
+public:
+    // Scene pass inputs that change without any frame request.
+    struct Key
+    {
+        std::array<unsigned int, 2> size{ { 0, 0 } };
+        Transform3d view_matrix{ Transform3d::Identity() };
+        Transform3d projection_matrix{ Transform3d::Identity() };
+        // Hovered volumes that draw their sinking contour, hovered plate icons, hovered gizmo grabber.
+        std::vector<int> sinking_hover_volume_idxs;
+        std::vector<int> hover_plate_icon_idxs;
+        int gizmo_hover_id{ -1 };
+        bool render_preview{ true };
+
+        bool operator == (const Key& other) const {
+            return size == other.size && render_preview == other.render_preview &&
+                   gizmo_hover_id == other.gizmo_hover_id &&
+                   sinking_hover_volume_idxs == other.sinking_hover_volume_idxs &&
+                   hover_plate_icon_idxs == other.hover_plate_icon_idxs &&
+                   view_matrix.isApprox(other.view_matrix) &&
+                   projection_matrix.isApprox(other.projection_matrix);
+        }
+    };
+
+    // Copies the bound read framebuffer, sized by key.size, and remembers key.
+    void capture(Key key);
+    bool matches(const Key& key) const { return m_valid && m_key == key; }
+    // Draws the last capture over the whole viewport, on the given full screen quad.
+    void render(GLModel& quad);
+    void invalidate() { m_valid = false; }
+    // Frees the texture.
+    void reset();
+
+private:
+    unsigned int m_texture_id{ 0 };
+    std::array<unsigned int, 2> m_texture_size{ { 0, 0 } };
+    Key m_key;
+    bool m_valid{ false };
+};
+
+} // namespace GUI
+} // namespace Slic3r