Improved visibility of brush, eraser, and selection tools

src/CanvasTheme.cpp

@@ -7,6 +7,32 @@
 
 using namespace NetworkingObjects;
 
+const char* visibleBlendModeCode = R"V(
+	vec4 main(vec4 src, vec4 dst) {
+        float value = max(max(dst.x, dst.y), dst.z) / dst.a;
+        vec4 actualSrc;
+        if(value > 0.6)
+            actualSrc = vec4(vec3(0.0), src.a);
+        else
+            actualSrc = vec4(src.a);
+        return actualSrc + (1.0 - actualSrc.a) * dst;
+    }
+)V";
+
+sk_sp<SkBlender> CanvasTheme::get_visible_blend_mode() {
+    static sk_sp<SkBlender> blender = nullptr;
+    if(!blender) {
+        auto effect = SkRuntimeEffect::MakeForBlender(SkString(visibleBlendModeCode));
+  	    if(!effect.effect) {
+            std::cout << "[CanvasTheme::get_visible_blend_mode] " << " blender construction error\n";
+            std::cout << effect.errorText.c_str() << std::endl;
+            throw std::runtime_error("Shader Compile Failure");
+        }
+        blender = effect.effect->makeBlender(nullptr);
+    }
+    return blender;
+}
+
 CanvasTheme::CanvasTheme(World& w):
     world(w)
 {}
@@ -37,13 +63,11 @@ void CanvasTheme::set_back_color(const Vector3f& newBackColor) {
 
 void CanvasTheme::set_tool_front_color(DrawingProgram& drawP) {
     Vector3f newHSV = rgb_to_hsv<Vector3f>(backColor->c);
-    SkColor4f oldToolFrontColor = toolFrontColor;
     if(newHSV.z() >= 0.6f)
         toolFrontColor = SkColor4f{0.0f, 0.0f, 0.0f, 1.0f};
     else
         toolFrontColor = SkColor4f{1.0f, 1.0f, 1.0f, 1.0f};
-    if(oldToolFrontColor != toolFrontColor)
-        drawP.drawCache.clear_own_cached_surfaces();
+    drawP.drawCache.clear_own_cached_surfaces();
 }
 
 void CanvasTheme::register_class() {

src/CanvasTheme.hpp

@@ -6,6 +6,8 @@
 #include <Helpers/Serializers.hpp>
 #include <Helpers/VersionNumber.hpp>
 
+#include <include/effects/SkRuntimeEffect.h>
+
 class DrawingProgram;
 class World;
 
@@ -21,6 +23,9 @@ class CanvasTheme {
         void write_create_message(cereal::PortableBinaryOutputArchive& a) const;
         void save_file(cereal::PortableBinaryOutputArchive& a) const;
         void load_file(cereal::PortableBinaryInputArchive& a, VersionNumber version);
+
+        static sk_sp<SkBlender> get_visible_blend_mode();
+
     private:
         void set_tool_front_color(DrawingProgram& drawP);
         struct BackColor {

src/DrawingProgram/DrawingProgram.cpp

@@ -522,6 +522,7 @@ SkPaint DrawingProgram::select_tool_line_paint() {
     selectLinePaint.setStrokeWidth(3);
     selectLinePaint.setColor4f(world.canvasTheme.get_tool_front_color());
     selectLinePaint.setPathEffect(lassoLineDashEffect);
+    selectLinePaint.setBlender(CanvasTheme::get_visible_blend_mode());
 
     return selectLinePaint;
 }

src/DrawingProgram/Tools/BrushTool.cpp

@@ -187,17 +187,21 @@ void BrushTool::draw(SkCanvas* canvas, const DrawData& drawData) {
     if(!drawP.world.main.input.isTouchDevice && drawData.main->world->drawProg.controls.cursorHoveringOverCanvas) {
         auto relativeWidthResult = drawP.world.main.toolConfig.get_relative_width_stroke_size(drawP, drawP.world.drawData.cam.c.inverseScale);
         if(relativeWidthResult.first.has_value()) {
-            SkPaint linePaint;
-            linePaint.setColor4f(drawP.world.canvasTheme.get_tool_front_color());
-            linePaint.setStroke(true);
-            linePaint.setStrokeWidth(0.0f);
             float width = relativeWidthResult.first.value();
             if(objInfoBeingEdited)
                 width *= penWidth * 0.5f;
             else
                 width *= 0.5f;
+            width += 1.0f;
             Vector2f pos = drawData.main->input.mouse.pos;
-            canvas->drawCircle(pos.x(), pos.y(), width, linePaint);
+            SkPaint linePaint;
+            linePaint.setColor4f({1.0f, 1.0f, 1.0f, 1.0f});
+            linePaint.setStyle(SkPaint::kStroke_Style);
+            linePaint.setStrokeCap(SkPaint::kRound_Cap);
+            linePaint.setStrokeWidth(0.0f);
+            linePaint.setBlender(CanvasTheme::get_visible_blend_mode());
+            SkPath circ = SkPath::Circle(pos.x(), pos.y(), width);
+            canvas->drawPath(circ, linePaint);
         }
     }
 }

src/DrawingProgram/Tools/EraserTool.cpp

@@ -2,6 +2,7 @@
 #include "../DrawingProgram.hpp"
 #include "../../MainProgram.hpp"
 #include "../../DrawData.hpp"
+#include <include/core/SkBlendMode.h>
 #include <include/core/SkPathBuilder.h>
 
 EraserTool::EraserTool(DrawingProgram& initDrawP):
@@ -118,14 +119,12 @@ void EraserTool::draw(SkCanvas* canvas, const DrawData& drawData) {
         auto relativeWidthResult = drawP.world.main.toolConfig.get_relative_width_stroke_size(drawP, drawP.world.drawData.cam.c.inverseScale);
         if(relativeWidthResult.first.has_value()) {
             float width = relativeWidthResult.first.value() * 0.5f;
-            SkColor4f c = drawP.world.canvasTheme.get_tool_front_color();
-            c.fA = 0.5f;
-
             SkPaint linePaint;
-            linePaint.setColor4f(c);
+            linePaint.setColor4f({1.0f, 1.0f, 1.0f, 0.5f});
             linePaint.setStyle(SkPaint::kStroke_Style);
             linePaint.setStrokeCap(SkPaint::kRound_Cap);
             linePaint.setStrokeWidth(width * 2.0f);
+            linePaint.setBlender(CanvasTheme::get_visible_blend_mode());
             SkPathBuilder erasePath;
             erasePath.moveTo(convert_vec2<SkPoint>(lastPos));
             erasePath.lineTo(convert_vec2<SkPoint>(drawData.main->input.mouse.pos));