Fixed assert in Canvas::drawVertices (#208)

Added a test for Canvas::drawVertices

skiko/src/commonMain/kotlin/org/jetbrains/skia/Canvas.kt

@@ -852,8 +852,16 @@ open class Canvas internal constructor(ptr: NativePointer, managed: Boolean, int
         mode: BlendMode,
         paint: Paint
     ): Canvas {
-        require(colors == null || colors.size == positions.size) { "Expected colors.length == positions.length, got: " + colors!!.size + " != " + positions.size }
-        require(texCoords == null || texCoords.size == positions.size) { "Expected texCoords.length == positions.length, got: " + texCoords!!.size + " != " + positions.size }
+        require(positions.size % 2 == 0) {
+            "Expected even number of positions: ${positions.size}"
+        }
+        val points = positions.size / 2
+        require(colors == null || colors.size == points) {
+            "Expected colors.length == positions.length / 2, got: " + colors!!.size + " != " + points
+        }
+        require(texCoords == null || texCoords.size == positions.size) {
+            "Expected texCoords.length == positions.length, got: " + texCoords!!.size + " != " + positions.size
+        }
         Stats.onNativeCall()
         interopScope {
             _nDrawVertices(

skiko/src/jvmTest/kotlin/org/jetbrains/skiko/CanvasTest.kt

+package org.jetbrains.skiko
+
+import org.jetbrains.skia.*
+import org.jetbrains.skiko.util.ScreenshotTestRule
+import org.junit.Rule
+import org.junit.Test
+
+class CanvasTest {
+    @get:Rule
+    val screenshots = ScreenshotTestRule()
+
+    @Test
+    fun drawVertices() {
+        val surface = Surface.makeRasterN32Premul(16, 16)
+
+        val positions = Point.flattenArray(
+            arrayOf(
+                Point(0f, 0f),
+                Point(16f, 0f),
+                Point(8f, 8f),
+                Point(16f, 8f),
+                Point(0f, 16f),
+                Point(16f, 16f),
+            )
+        )!!
+
+        val colors = listOf(
+            Color.RED, Color.GREEN, Color.BLUE, Color.CYAN, Color.MAGENTA, Color.YELLOW
+        ).toIntArray()
+
+        val indices = shortArrayOf(0, 1, 2, 3, 4, 5)
+
+        surface.canvas.drawVertices(
+            VertexMode.TRIANGLES,
+            positions,
+            colors,
+            positions,
+            indices,
+            BlendMode.SRC_OVER,
+            Paint()
+        )
+
+        screenshots.assert(surface.makeImageSnapshot())
+    }
+}