Route canvas cursor visibility through app core

src/app_core/canvas_tool_ui.h

@@ -2,6 +2,8 @@
 
 #include "foundation/result.h"
 
+#include <cmath>
+
 namespace pp::app {
 
 enum class CanvasToolOperation {
@@ -30,6 +32,13 @@ enum class CanvasToolTransformAction {
     cut,
 };
 
+enum class CanvasCursorVisibilityMode {
+    never,
+    small_brush,
+    not_painting,
+    always,
+};
+
 struct CanvasToolPlan {
     CanvasToolOperation operation = CanvasToolOperation::select_mode;
     CanvasToolMode mode = CanvasToolMode::draw;
@@ -59,6 +68,25 @@ struct CanvasToolButtonState {
     bool flood_fill_active = false;
 };
 
+struct CanvasCursorVisibilityInput {
+    CanvasToolMode mode = CanvasToolMode::draw;
+    CanvasCursorVisibilityMode visibility_mode = CanvasCursorVisibilityMode::never;
+    bool has_current_brush = true;
+    float brush_tip_size = 0.0F;
+    bool pen_is_drawing = false;
+    bool alt_down = false;
+    bool pen_is_resizing = false;
+    bool pen_is_picking = false;
+};
+
+struct CanvasCursorVisibilityPlan {
+    bool visible = true;
+    bool paint_mode = false;
+    bool uses_brush_size = false;
+    bool uses_pen_state = false;
+    bool forced_visible_by_modifier_or_tool = false;
+};
+
 class CanvasToolServices {
 public:
     virtual ~CanvasToolServices() = default;
@@ -134,6 +162,54 @@ public:
     return state;
 }
 
+[[nodiscard]] inline constexpr bool canvas_tool_mode_is_paint(CanvasToolMode mode) noexcept
+{
+    return mode == CanvasToolMode::draw || mode == CanvasToolMode::erase;
+}
+
+[[nodiscard]] inline pp::foundation::Result<CanvasCursorVisibilityPlan> plan_canvas_cursor_visibility(
+    const CanvasCursorVisibilityInput& input)
+{
+    CanvasCursorVisibilityPlan plan;
+    plan.paint_mode = canvas_tool_mode_is_paint(input.mode);
+    if (!plan.paint_mode) {
+        plan.visible = true;
+        return pp::foundation::Result<CanvasCursorVisibilityPlan>::success(plan);
+    }
+
+    switch (input.visibility_mode) {
+    case CanvasCursorVisibilityMode::always:
+        plan.visible = true;
+        break;
+    case CanvasCursorVisibilityMode::never:
+        plan.visible = false;
+        break;
+    case CanvasCursorVisibilityMode::small_brush:
+        if (!input.has_current_brush) {
+            return pp::foundation::Result<CanvasCursorVisibilityPlan>::failure(
+                pp::foundation::Status::invalid_argument("canvas cursor small-brush mode requires a current brush"));
+        }
+        if (!std::isfinite(input.brush_tip_size) || input.brush_tip_size < 0.0F) {
+            return pp::foundation::Result<CanvasCursorVisibilityPlan>::failure(
+                pp::foundation::Status::invalid_argument("canvas cursor brush size must be finite and non-negative"));
+        }
+        plan.visible = input.brush_tip_size < 10.0F;
+        plan.uses_brush_size = true;
+        break;
+    case CanvasCursorVisibilityMode::not_painting:
+        plan.visible = !input.pen_is_drawing;
+        plan.uses_pen_state = true;
+        break;
+    }
+
+    if (input.alt_down || input.pen_is_resizing || input.pen_is_picking) {
+        plan.visible = true;
+        plan.forced_visible_by_modifier_or_tool = true;
+    }
+
+    return pp::foundation::Result<CanvasCursorVisibilityPlan>::success(plan);
+}
+
 [[nodiscard]] inline pp::foundation::Status execute_canvas_tool_plan(
     const CanvasToolPlan& plan,
     CanvasToolServices& services)