Implement pen_changePenShadeBy block

scratchcpp · adazem009 · Mar 28, 2026 · Mar 21, 2026 · Mar 21, 2026 · Mar 21, 2026
commit e7b3ea70402fce30992f529a4bc62cc7c31cc8c3
diff --git a/src/blocks/penblocks.cpp b/src/blocks/penblocks.cpp
@@ -88,6 +88,7 @@ void PenBlocks::registerBlocks(IEngine *engine)
     engine->addCompileFunction(this, "pen_setPenColorParamTo", &compileSetPenColorParamTo);
     engine->addCompileFunction(this, "pen_changePenSizeBy", &compileChangePenSizeBy);
     engine->addCompileFunction(this, "pen_setPenSizeTo", &compileSetPenSizeTo);
+    engine->addCompileFunction(this, "pen_changePenShadeBy", &compileChangePenShadeBy);
 }
 
 CompilerValue *PenBlocks::compileClear(Compiler *compiler)
@@ -198,6 +199,14 @@ CompilerValue *PenBlocks::compileSetPenSizeTo(Compiler *compiler)
     return nullptr;
 }
 
+CompilerValue *PenBlocks::compileChangePenShadeBy(Compiler *compiler)
+{
+    CompilerValue *shade = compiler->addInput("SHADE");
+    CompilerValue *change = compiler->addConstValue(true);
+    compiler->addTargetFunctionCall("pen_set_or_change_pen_shade", Compiler::StaticType::Void, { Compiler::StaticType::Number, Compiler::StaticType::Bool }, { shade, change });
+    return nullptr;
+}
+
 static TargetModel *getTargetModel(Target *target)
 {
     if (target->isStage()) {
@@ -337,3 +346,62 @@ BLOCK_EXPORT void pen_setPenSizeTo(Target *target, double value)
     PenAttributes &penAttributes = getTargetModel(target)->penAttributes();
     penAttributes.diameter = std::clamp(value, PEN_SIZE_MIN, PEN_SIZE_MAX);
 }
+
+static QRgb mix_rgb(QRgb rgb0, QRgb rgb1, double fraction1)
+{
+    // https://github.com/scratchfoundation/scratch-vm/blob/a4f095db5e03e072ba222fe721eeeb543c9b9c15/src/util/color.js#L192-L201
+    // https://github.com/scratchfoundation/scratch-flash/blob/2e4a402ceb205a042887f54b26eebe1c2e6da6c0/src/util/Color.as#L75-L89
+    if (fraction1 <= 0)
+        return rgb0;
+
+    if (fraction1 >= 1)
+        return rgb1;
+
+    const double fraction0 = 1 - fraction1;
+    const int r = static_cast<int>(((fraction0 * qRed(rgb0)) + (fraction1 * qRed(rgb1)))) & 255;
+    const int g = static_cast<int>(((fraction0 * qGreen(rgb0)) + (fraction1 * qGreen(rgb1)))) & 255;
+    const int b = static_cast<int>(((fraction0 * qBlue(rgb0)) + (fraction1 * qBlue(rgb1)))) & 255;
+    return qRgb(r, g, b);
+}
+
+inline void legacy_update_pen_color(PenState &penState)
+{
+    // https://github.com/scratchfoundation/scratch-vm/blob/8dbcc1fc8f8d8c4f1e40629fe8a388149d6dfd1c/src/extensions/scratch3_pen/index.js#L750-L767
+    // Create the new color in RGB using the scratch 2 "shade" model
+    QRgb rgb = QColor::fromHsvF(penState.color / 100, 1, 1).rgb();
+    const double shade = (penState.shade > 100) ? 200 - penState.shade : penState.shade;
+
+    if (shade < 50)
+        rgb = mix_rgb(0, rgb, (10 + shade) / 60);
+    else
+        rgb = mix_rgb(rgb, 0xFFFFFF, (shade - 50) / 60);
+
+    // Update the pen state according to new color
+    QColor hsv = QColor::fromRgb(rgb).toHsv();
+    penState.color = 100 * hsv.hueF();
+    penState.saturation = 100 * hsv.saturationF();
+    penState.brightness = 100 * hsv.valueF();
+
+    penState.updateColor();
+}
+
+BLOCK_EXPORT void pen_set_or_change_pen_shade(Target *target, double shade, bool change)
+{
+    // https://github.com/scratchfoundation/scratch-vm/blob/8dbcc1fc8f8d8c4f1e40629fe8a388149d6dfd1c/src/extensions/scratch3_pen/index.js#L718-L730
+    PenState &penState = getTargetModel(target)->penState();
+
+    if (change)
+        shade += penState.shade;
+
+    // Wrap clamp the new shade value the way Scratch 2 did
+    const double hi = 200.0;
+    shade = fmod(shade, hi);
+
+    if (shade < 0)
+        shade += hi;
+
+    // And store the shade that was used to compute this new color for later use
+    penState.shade = shade;
+
+    legacy_update_pen_color(penState);
+}
diff --git a/src/blocks/penblocks.h b/src/blocks/penblocks.h
@@ -23,6 +23,7 @@ class PenBlocks : public libscratchcpp::IExtension
         static libscratchcpp::CompilerValue *compileSetPenColorParamTo(libscratchcpp::Compiler *compiler);
         static libscratchcpp::CompilerValue *compileChangePenSizeBy(libscratchcpp::Compiler *compiler);
         static libscratchcpp::CompilerValue *compileSetPenSizeTo(libscratchcpp::Compiler *compiler);
+        static libscratchcpp::CompilerValue *compileChangePenShadeBy(libscratchcpp::Compiler *compiler);
 };
 
 } // namespace scratchcpprender
diff --git a/test/blocks/pen_blocks_test.cpp b/test/blocks/pen_blocks_test.cpp
@@ -2202,3 +2202,147 @@ TEST_F(PenBlocksTest, SetPenSizeTo_Stage)
     thread->run();
     ASSERT_EQ(model.penAttributes().diameter, 511.5);
 }
+
+TEST_F(PenBlocksTest, ChangePenShadeBy)
+{
+    auto sprite = std::make_shared<Sprite>();
+    sprite->setEngine(&m_engineMock);
+
+    RenderedTarget renderedTarget;
+    SpriteModel model;
+    model.init(sprite.get());
+    model.setRenderedTarget(&renderedTarget);
+    sprite->setInterface(&model);
+
+    ScriptBuilder builder(m_extension.get(), m_engine, sprite);
+    builder.addBlock("pen_changePenShadeBy");
+    builder.addValueInput("SHADE", 49.2);
+
+    PenState &penState = model.penState();
+    penState.color = 60;
+    penState.saturation = 90;
+    penState.brightness = 75;
+    penState.shade = 13.8;
+    penState.updateColor();
+
+    auto original = model.penAttributes().color;
+
+    auto thread = buildScript(builder, sprite.get());
+
+    EXPECT_CALL(m_engineMock, requestRedraw).Times(0);
+    thread->run();
+
+    EXPECT_EQ(model.penAttributes().color.red(), 55);
+    EXPECT_EQ(model.penAttributes().color.green(), 135);
+    EXPECT_EQ(model.penAttributes().color.blue(), 255);
+    EXPECT_EQ(model.penAttributes().color.alpha(), 255);
+    EXPECT_EQ(model.penState().shade, 63);
+}
+
+TEST_F(PenBlocksTest, ChangePenShadeBy_OutOfRange)
+{
+    auto sprite = std::make_shared<Sprite>();
+    sprite->setEngine(&m_engineMock);
+
+    RenderedTarget renderedTarget;
+    SpriteModel model;
+    model.init(sprite.get());
+    model.setRenderedTarget(&renderedTarget);
+    sprite->setInterface(&model);
+
+    ScriptBuilder builder(m_extension.get(), m_engine, sprite);
+    builder.addBlock("pen_changePenShadeBy");
+    builder.addValueInput("SHADE", 189.6);
+
+    PenState &penState = model.penState();
+    penState.color = 60;
+    penState.saturation = 90;
+    penState.brightness = 75;
+    penState.shade = 13.8;
+    penState.updateColor();
+
+    auto original = model.penAttributes().color;
+
+    auto thread = buildScript(builder, sprite.get());
+
+    EXPECT_CALL(m_engineMock, requestRedraw).Times(0);
+    thread->run();
+
+    EXPECT_EQ(model.penAttributes().color.red(), 0);
+    EXPECT_EQ(model.penAttributes().color.green(), 22);
+    EXPECT_EQ(model.penAttributes().color.blue(), 56);
+    EXPECT_EQ(model.penAttributes().color.alpha(), 255);
+    EXPECT_EQ(std::round(model.penState().shade * 100) / 100, 3.4);
+}
+
+TEST_F(PenBlocksTest, ChangePenShadeBy_OutOfRange_Negative)
+{
+    auto sprite = std::make_shared<Sprite>();
+    sprite->setEngine(&m_engineMock);
+
+    RenderedTarget renderedTarget;
+    SpriteModel model;
+    model.init(sprite.get());
+    model.setRenderedTarget(&renderedTarget);
+    sprite->setInterface(&model);
+
+    ScriptBuilder builder(m_extension.get(), m_engine, sprite);
+    builder.addBlock("pen_changePenShadeBy");
+    builder.addValueInput("SHADE", -25.3);
+
+    PenState &penState = model.penState();
+    penState.color = 60;
+    penState.saturation = 90;
+    penState.brightness = 75;
+    penState.shade = 13.8;
+    penState.updateColor();
+
+    auto original = model.penAttributes().color;
+
+    auto thread = buildScript(builder, sprite.get());
+
+    EXPECT_CALL(m_engineMock, requestRedraw).Times(0);
+    thread->run();
+
+    EXPECT_EQ(model.penAttributes().color.red(), 0);
+    EXPECT_EQ(model.penAttributes().color.green(), 36);
+    EXPECT_EQ(model.penAttributes().color.blue(), 91);
+    EXPECT_EQ(model.penAttributes().color.alpha(), 255);
+    EXPECT_EQ(model.penState().shade, 188.5);
+}
+
+TEST_F(PenBlocksTest, ChangePenShadeBy_Stage)
+{
+    auto stage = std::make_shared<Stage>();
+    stage->setEngine(&m_engineMock);
+
+    RenderedTarget renderedTarget;
+    StageModel model;
+    model.init(stage.get());
+    model.setRenderedTarget(&renderedTarget);
+    stage->setInterface(&model);
+
+    ScriptBuilder builder(m_extension.get(), m_engine, stage);
+    builder.addBlock("pen_changePenShadeBy");
+    builder.addValueInput("SHADE", 49.2);
+
+    PenState &penState = model.penState();
+    penState.color = 60;
+    penState.saturation = 90;
+    penState.brightness = 75;
+    penState.shade = 13.8;
+    penState.updateColor();
+
+    auto original = model.penAttributes().color;
+
+    auto thread = buildScript(builder, stage.get());
+
+    EXPECT_CALL(m_engineMock, requestRedraw).Times(0);
+    thread->run();
+
+    EXPECT_EQ(model.penAttributes().color.red(), 55);
+    EXPECT_EQ(model.penAttributes().color.green(), 135);
+    EXPECT_EQ(model.penAttributes().color.blue(), 255);
+    EXPECT_EQ(model.penAttributes().color.alpha(), 255);
+    EXPECT_EQ(model.penState().shade, 63);
+}