adds new way to add textureholder

ios/graphics/Texture/TextureHolder.swift

@@ -75,6 +75,51 @@ public class TextureHolder: NSObject {
         let texture = try MetalContext.current.textureLoader.newTexture(data: data, options: options)
         self.init(texture, textureUsableSize: textureUsableSize)
     }
+
+    public convenience init(_ size: CGSize, drawCallback: ((CGContext) -> Void)) throws {
+        guard size.width > 0, size.height > 0 else {
+            throw TextureHolderError.emptyData
+        }
+
+        let width : Int = Int(size.width)
+        let height : Int = Int(size.height)
+
+        let bytesPerPixel = 4
+        let bytesPerRow = bytesPerPixel * width
+
+        let td = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: .rgba8Unorm, width: width, height: height, mipmapped: false)
+        td.usage = .shaderRead
+
+        guard let texture = MetalContext.current.device.makeTexture(descriptor: td) else {
+            throw TextureHolderError.emptyData
+        }
+
+        let length = 4 * width * height
+        guard let imageData = calloc(width * height, 4) else {
+            throw TextureHolderError.emptyData
+        }
+
+        let data = NSMutableData(bytesNoCopy: imageData, length: length, freeWhenDone: true)
+
+        let colorSpace = CGColorSpaceCreateDeviceRGB()
+        let bitmapInfo = CGBitmapInfo(rawValue: CGBitmapInfo.byteOrder32Big.rawValue | CGImageAlphaInfo.premultipliedLast.rawValue)
+
+        guard let context = CGContext(data: data.mutableBytes, width: width, height: height, bitsPerComponent: 8, bytesPerRow: 4 * width, space: colorSpace, bitmapInfo: bitmapInfo.rawValue) else {
+            throw TextureHolderError.emptyData
+        }
+
+        context.translateBy(x: 0, y: size.height)
+        context.scaleBy(x: 1.0, y: -1.0)
+
+        UIGraphicsPushContext(context)
+        drawCallback(context)
+        UIGraphicsPopContext()
+
+        let region = MTLRegionMake2D(0, 0, width, height)
+        texture.replace(region: region, mipmapLevel: 0, withBytes: data.bytes, bytesPerRow: bytesPerRow)
+
+        self.init(texture, textureUsableSize: nil)
+    }
 }
 
 extension TextureHolder: MCTextureHolderInterface {