Support linear gradient paint

Fixes Nyan Progress Bar, for example

Author: SerVB

projector-client-common/src/commonMain/kotlin/org/jetbrains/projector/client/common/Renderer.kt

@@ -260,10 +260,10 @@ class Renderer(private val renderingSurface: RenderingSurface) {
     requestedState.paint = color.toColor()
   }
 
-  fun setGradientPaint(p1: Point, p2: Point, color1: Int, color2: Int) {
-    val linearGradient = ctx.createLinearGradient(p1.x, p1.y, p2.x, p2.y).apply {
-      addColorStop(0.0, color1)
-      addColorStop(1.0, color2)
+  fun setGradientPaint(p1: Point, p2: Point, fractions: List<Double>, argbs: List<Int>) {
+    val linearGradient = ctx.createLinearGradient(p1.x, p1.y, p2.x, p2.y)
+    fractions.zip(argbs).forEach { (fraction, argb) ->
+      linearGradient.addColorStop(fraction, argb)
     }
 
     requestedState.paint = linearGradient

projector-client-common/src/commonMain/kotlin/org/jetbrains/projector/client/common/SingleRenderingSurfaceProcessor.kt

@@ -73,8 +73,8 @@ class SingleRenderingSurfaceProcessor(private val renderingSurface: RenderingSur
               is PaintValue.Gradient -> renderer.setGradientPaint(
                 p1 = paintValue.p1,
                 p2 = paintValue.p2,
-                color1 = paintValue.argb1,
-                color2 = paintValue.argb2
+                fractions = paintValue.fractions,
+                argbs = paintValue.argbs,
               )
 
               is PaintValue.Unknown -> logUnsupportedCommand(it)

projector-client-web/src/main/kotlin/org/jetbrains/projector/client/web/protocol/ManualJsonToClientMessageDecoder.kt

@@ -332,7 +332,7 @@ object ManualJsonToClientMessageDecoder : ToClientMessageDecoder {
       "a" -> content.toColor()
       "b" -> PaintValue.Gradient(
         content["a"].unsafeCast<Json>().toPoint(), content["b"].unsafeCast<Json>().toPoint(),
-        content["c"] as Int, content["d"] as Int
+        content["c"].unsafeCast<Array<Double>>().toList(), content["d"].unsafeCast<Array<Int>>().toList(),
       )
       "c" -> PaintValue.Unknown(content["a"] as String)
       else -> throw IllegalArgumentException("Unsupported paint value type: ${JSON.stringify(this)}")

projector-common/src/commonMain/kotlin/org/jetbrains/projector/common/protocol/data/PaintValue.kt

@@ -44,9 +44,9 @@ sealed class PaintValue {
     @SerialName("b")
     val p2: Point,
     @SerialName("c")
-    val argb1: Int,
+    val fractions: List<Double>,
     @SerialName("d")
-    val argb2: Int,
+    val argbs: List<Int>,
   ) : PaintValue()
 
   @Serializable

projector-common/src/commonMain/kotlin/org/jetbrains/projector/common/protocol/handshake/Constant.kt

@@ -63,4 +63,5 @@ val commonVersionList = listOf(
   -1867356666,
   1741530029,
   2040465192,
+  -795345262,
 )

projector-server-core/src/main/kotlin/org/jetbrains/projector/server/core/convert/toClient/Convert.kt

@@ -169,8 +169,15 @@ public fun Paint.toPaintValue(): PaintValue = when (this) {
   is GradientPaint -> PaintValue.Gradient(
     p1 = point1.toPoint(),
     p2 = point2.toPoint(),
-    argb1 = color1.rgb,
-    argb2 = color2.rgb
+    fractions = listOf(0.0, 1.0),
+    argbs = listOf(color1.rgb, color2.rgb),
+  )
+
+  is LinearGradientPaint -> PaintValue.Gradient(
+    p1 = startPoint.toPoint(),
+    p2 = endPoint.toPoint(),
+    fractions = fractions.map(Float::toDouble),
+    argbs = colors.map { it.rgb },
   )
 
   is MultipleGradientPaint -> PaintValue.Unknown("MultipleGradientPaint, maybe split to Linear and Radial")