Switching to "random backdrop" should always select a different backdrop (Closes #521)

src/blocks/looksblocks.cpp

@@ -964,8 +964,9 @@ void LooksBlocks::randomBackdropImpl(VirtualMachine *vm)
     if (Stage *stage = vm->engine()->stage()) {
         std::size_t count = stage->costumes().size();
 
-        if (count > 0)
-            stage->setCostumeIndex(rng->randint(0, count - 1));
+        if (count > 1) {
+            stage->setCostumeIndex(rng->randintExcept(0, count - 1, stage->costumeIndex()));
+        }
     }
 }
 

src/engine/internal/irandomgenerator.h

@@ -12,6 +12,7 @@ class IRandomGenerator
 
         virtual long randint(long start, long end) const = 0;
         virtual double randintDouble(double start, double end) const = 0;
+        virtual long randintExcept(long start, long end, long except) const = 0;
 };
 
 } // namespace libscratchcpp

src/engine/internal/randomgenerator.cpp

@@ -41,3 +41,29 @@ double RandomGenerator::randintDouble(double start, double end) const
     std::uniform_real_distribution<double> distribution(start, end);
     return distribution(*m_generator);
 }
+
+long RandomGenerator::randintExcept(long start, long end, long except) const
+{
+    if (start > end) {
+        std::swap(start, end);
+    }
+
+    if (except < start || except > end) {
+        return randint(start, end);
+    } else if (start == end) {
+        return start;
+    } else if (end - start == 1) {
+        if (except == start)
+            return end;
+        else
+            return start;
+    }
+
+    if (randint(0, 1) == 0) {
+        std::uniform_int_distribution<long> distribution(start, except - 1);
+        return distribution(*m_generator);
+    } else {
+        std::uniform_int_distribution<long> distribution(except + 1, end);
+        return distribution(*m_generator);
+    }
+}

src/engine/internal/randomgenerator.h

@@ -20,6 +20,7 @@ class RandomGenerator : public IRandomGenerator
 
         long randint(long start, long end) const override;
         double randintDouble(double start, double end) const override;
+        long randintExcept(long start, long end, long except) const;
 
     private:
         static std::shared_ptr<RandomGenerator> m_instance;

test/blocks/looks_blocks_test.cpp

@@ -1992,7 +1992,7 @@ TEST_F(LooksBlocksTest, SwitchBackdropToImpl)
     LooksBlocks::rng = &rng;
 
     EXPECT_CALL(m_engineMock, startBackdropScripts(stage.costumeAt(3)->broadcast(), &thread, false));
-    EXPECT_CALL(rng, randint(0, 5)).WillOnce(Return(3));
+    EXPECT_CALL(rng, randintExcept(0, 5, 0)).WillOnce(Return(3));
     stage.setCostumeIndex(0);
     vm->setBytecode(bytecode15);
     vm->run();
@@ -2001,7 +2001,7 @@ TEST_F(LooksBlocksTest, SwitchBackdropToImpl)
     ASSERT_EQ(stage.costumeIndex(), 3);
 
     EXPECT_CALL(m_engineMock, startBackdropScripts(stage.costumeAt(5)->broadcast(), &thread, false));
-    EXPECT_CALL(rng, randint(0, 5)).WillOnce(Return(5));
+    EXPECT_CALL(rng, randintExcept(0, 5, 3)).WillOnce(Return(5));
     vm->reset();
     vm->run();
 
@@ -2011,7 +2011,7 @@ TEST_F(LooksBlocksTest, SwitchBackdropToImpl)
     stage.addCostume(std::make_shared<Costume>("random backdrop", "b7", "svg"));
 
     EXPECT_CALL(m_engineMock, startBackdropScripts(stage.costumeAt(6)->broadcast(), &thread, false));
-    EXPECT_CALL(rng, randint).Times(0);
+    EXPECT_CALL(rng, randintExcept).Times(0);
     vm->reset();
     vm->run();
 
@@ -2337,7 +2337,7 @@ TEST_F(LooksBlocksTest, SwitchBackdropToAndWaitImpl)
     LooksBlocks::rng = &rng;
 
     EXPECT_CALL(m_engineMock, startBackdropScripts(stage.costumeAt(3)->broadcast(), &thread, true));
-    EXPECT_CALL(rng, randint(0, 5)).WillOnce(Return(3));
+    EXPECT_CALL(rng, randintExcept(0, 5, 0)).WillOnce(Return(3));
     stage.setCostumeIndex(0);
     vm->resolvePromise();
     vm->setBytecode(bytecode15);
@@ -2349,7 +2349,7 @@ TEST_F(LooksBlocksTest, SwitchBackdropToAndWaitImpl)
     ASSERT_EQ(stage.costumeIndex(), 3);
 
     EXPECT_CALL(m_engineMock, startBackdropScripts(stage.costumeAt(5)->broadcast(), &thread, true));
-    EXPECT_CALL(rng, randint(0, 5)).WillOnce(Return(5));
+    EXPECT_CALL(rng, randintExcept(0, 5, 3)).WillOnce(Return(5));
     vm->reset();
     vm->run();
     vm->resolvePromise();
@@ -2361,7 +2361,7 @@ TEST_F(LooksBlocksTest, SwitchBackdropToAndWaitImpl)
     stage.addCostume(std::make_shared<Costume>("random backdrop", "b7", "svg"));
 
     EXPECT_CALL(m_engineMock, startBackdropScripts(stage.costumeAt(6)->broadcast(), &thread, true));
-    EXPECT_CALL(rng, randint).Times(0);
+    EXPECT_CALL(rng, randintExcept).Times(0);
     vm->reset();
     vm->run();
     vm->resolvePromise();
@@ -2488,16 +2488,17 @@ TEST_F(LooksBlocksTest, RandomBackdrop)
     RandomGeneratorMock rng;
     LooksBlocks::rng = &rng;
 
-    EXPECT_CALL(rng, randint).Times(0);
+    EXPECT_CALL(rng, randintExcept).Times(0);
     vm->run();
 
     ASSERT_EQ(vm->registerCount(), 0);
 
     stage.addCostume(std::make_shared<Costume>("backdrop1", "b1", "svg"));
     stage.addCostume(std::make_shared<Costume>("backdrop2", "b2", "svg"));
     stage.addCostume(std::make_shared<Costume>("backdrop3", "b3", "svg"));
+    stage.setCostumeIndex(0);
 
-    EXPECT_CALL(rng, randint(0, 2)).WillOnce(Return(1));
+    EXPECT_CALL(rng, randintExcept(0, 2, 0)).WillOnce(Return(1));
     EXPECT_CALL(m_engineMock, startBackdropScripts(stage.costumeAt(1)->broadcast(), &thread, false));
     vm->reset();
     vm->run();
@@ -2507,7 +2508,7 @@ TEST_F(LooksBlocksTest, RandomBackdrop)
 
     stage.addCostume(std::make_shared<Costume>("backdrop4", "b4", "svg"));
 
-    EXPECT_CALL(rng, randint(0, 3)).WillOnce(Return(2));
+    EXPECT_CALL(rng, randintExcept(0, 3, 1)).WillOnce(Return(2));
     EXPECT_CALL(m_engineMock, startBackdropScripts(stage.costumeAt(2)->broadcast(), &thread, false));
     vm->reset();
     vm->run();

test/mocks/randomgeneratormock.h

@@ -10,4 +10,5 @@ class RandomGeneratorMock : public IRandomGenerator
     public:
         MOCK_METHOD(long, randint, (long, long), (const, override));
         MOCK_METHOD(double, randintDouble, (double, double), (const, override));
+        MOCK_METHOD(long, randintExcept, (long, long, long), (const, override));
 };

test/randomgenerator/randomgenerator_test.cpp

@@ -43,3 +43,57 @@ TEST(RandomGeneratorTest, RandIntDouble)
         ASSERT_LE(num, 5.081);
     }
 }
+
+TEST(RandomGeneratorTest, RandIntExcept)
+{
+    auto rng = RandomGenerator::instance();
+    ASSERT_TRUE(rng);
+
+    long num;
+
+    for (int i = 0; i < 25; i++) {
+        num = rng->randintExcept(-2, 3, 0);
+        ASSERT_GE(num, -2);
+        ASSERT_LE(num, 3);
+        ASSERT_NE(num, 0);
+    }
+
+    for (int i = 0; i < 25; i++) {
+        num = rng->randintExcept(5, -3, 2);
+        ASSERT_GE(num, -3);
+        ASSERT_LE(num, 5);
+        ASSERT_NE(num, 2);
+    }
+
+    for (int i = 0; i < 25; i++) {
+        num = rng->randintExcept(5, 8, 2);
+        ASSERT_GE(num, 5);
+        ASSERT_LE(num, 8);
+    }
+
+    for (int i = 0; i < 25; i++) {
+        num = rng->randintExcept(5, 8, 10);
+        ASSERT_GE(num, 5);
+        ASSERT_LE(num, 8);
+    }
+
+    for (int i = 0; i < 25; i++) {
+        num = rng->randintExcept(2, 2, 2);
+        ASSERT_EQ(num, 2);
+    }
+
+    for (int i = 0; i < 25; i++) {
+        num = rng->randintExcept(2, 2, 5);
+        ASSERT_EQ(num, 2);
+    }
+
+    for (int i = 0; i < 25; i++) {
+        num = rng->randintExcept(1, 2, 1);
+        ASSERT_EQ(num, 2);
+    }
+
+    for (int i = 0; i < 25; i++) {
+        num = rng->randintExcept(1, 2, 2);
+        ASSERT_EQ(num, 1);
+    }
+}