improve gexit with init function and add basic mlx image gestion

libs/minilibx-macos/mlx_image.swift

@@ -0,0 +1,48 @@
+
+
+import Metal
+
+
+public class MlxImg
+{
+    public var texture: MTLTexture
+///    var texture_buff: MTLBuffer
+
+    public var texture_sizeline: Int
+    public var texture_data: UnsafeMutablePointer<UInt32>
+    public var texture_width: Int
+    public var texture_height: Int
+
+    public var onGPU = 0
+
+     convenience public init(d device:MTLDevice, w width:Int, h height:Int)
+     {
+	self.init(d:device, w:width, h:height, t:0)
+     }
+
+     public init(d device:MTLDevice, w width:Int, h height:Int, t target:Int)
+     {
+	 texture_width = width
+    	 texture_height = height
+    	 texture_sizeline = width * 4
+    	 texture_sizeline = 256 * (texture_sizeline / 256 + (texture_sizeline%256 >= 1 ? 1 : 0) )
+
+         let textureDesc = MTLTextureDescriptor()
+    	 textureDesc.width = texture_width
+    	 textureDesc.height = texture_height
+	 textureDesc.usage = .shaderRead
+	 if (target == 1)
+	  {
+		textureDesc.usage = .renderTarget
+		textureDesc.storageMode = .private
+	  }
+    	 textureDesc.pixelFormat = MTLPixelFormat.bgra8Unorm
+    	 let texture_buff = device.makeBuffer(length: texture_sizeline * height)!
+    	 texture = texture_buff.makeTexture(descriptor:textureDesc, offset:0, bytesPerRow:texture_sizeline)!	
+
+	let tmpptr = texture_buff.contents()
+	texture_data = tmpptr.assumingMemoryBound(to:UInt32.self)
+     }
+
+
+}