Question

我遇到了问题，在发布此处之前，我一直在寻找解决方案。

问题在于Monotouch中的透明PNG文件：

我正在尝试在上下文中加载透明PNG ，以便读取和写入像素颜色。我正在使用下面的代码，它与非透明的PNG完美配合。（我还试图在尝试获得正确的结果时进行其他几次尝试）

对于透明的PNG，问题似乎是我必须使用预乘的alpha信息（ CGImageAlphaInfo.PremultipliedLast ）在上下文中加载图像。这会导致RGB值在上下文中加载时从其原始值更改。

我尝试用 CGImageAlphaInfo.Last 创建一个上下文（理论上是正确的），但是我得到了一个异常（不可接受的参数组合）。

我想过尝试使用CoreImage，但这会限制我们的用户使用iOS 5或更高版本，我认为这是不可接受的。

我迫切需要找到一种方法来获取和设置透明PNG中的像素，因为我正在创建一个需要处理透明PNG的跨平台软件（使用MonoMac和Windows的iPhone，iPad，Mac）。

任何帮助将不胜感激。谢谢！

using System;
using System.Collections.Generic;
using System.Linq;
using MonoTouch.Foundation;
using MonoTouch.UIKit;
using System.Drawing;
using MonoTouch.CoreGraphics;
using System.Runtime.InteropServices;
using MonoTouch.CoreImage;

namespace TestPNG
{
    // The UIApplicationDelegate for the application. This class is responsible for launching the 
    // User Interface of the application, as well as listening (and optionally responding) to 
    // application events from iOS.
    [Register ("AppDelegate")]
    public partial class AppDelegate : UIApplicationDelegate
    {
        // class-level declarations
        UIWindow window;
        TestPNGViewController viewController;

        //
        // This method is invoked when the application has loaded and is ready to run. In this 
        // method you should instantiate the window, load the UI into it and then make the window
        // visible.
        //
        // You have 17 seconds to return from this method, or iOS will terminate your application.
        //
        public override bool FinishedLaunching (UIApplication app, NSDictionary options)
        {
            window = new UIWindow (UIScreen.MainScreen.Bounds);

            viewController = new TestPNGViewController ();
            window.RootViewController = viewController;
            window.MakeKeyAndVisible ();

            UIImage _CarrierImage = UIImage.FromFile ("Blue50.png");

            int width = _CarrierImage.CGImage.Width;
            int height = _CarrierImage.CGImage.Height;
            CGImage cg = _CarrierImage.CGImage;
            Console.WriteLine ("width: " + width.ToString ("000") + ", height: " + height.ToString ("000"));
            Console.WriteLine ("BitsPerComponent: " + cg.BitsPerComponent.ToString ());
            Console.WriteLine ("BytesPerRow: " + cg.BytesPerRow.ToString ());
            Console.WriteLine ("BitsPerPixel: " + cg.BitsPerPixel.ToString ());
            Console.WriteLine ("ColorSpace: " + cg.ColorSpace.ToString ());
            Console.WriteLine ("For image Blue0.png should have values: R:0, G:0, B:255, A: 0");
            Console.WriteLine ("For image Blue50.png should have values: R:0, G:0, B:255, A: 128");
            Console.WriteLine ("For image Blue100.png should have values: R:0, G:0, B:255, A: 255");

            // METHOD 1
//          CGDataProvider p = CGDataProvider.FromFile("Blue50.png");
//          CGImage cgimg = CGImage.FromPNG(p,null,false,CGColorRenderingIntent.Default);
//          UIImage _CarrierImage = new UIImage(cgimg);


            // METHOD 2
//          NSData dt = _CarrierImage.AsPNG();
//          IntPtr bitmapData = dt.Bytes;
//          
//          Console.WriteLine("Length: " + dt.Length.ToString());
//          for (int i=0; i < dt.Length; i++)
//          {
//              Console.WriteLine("i: " + i.ToString("00") + ", byte: " + dt[i].ToString());
//          }
//          


            // METHOD 3
//          UIGraphics.BeginImageContext (_CarrierImage.Size);
//          CGContext ctx = UIGraphics.GetCurrentContext ();
//          ctx.DrawImage (new RectangleF (0, 0, _CarrierImage.Size.Width, _CarrierImage.Size.Height), _CarrierImage.CGImage);
//          IntPtr dt = ctx.Handle;
//          for (int i=0; i < 100; i++)
//          {
//              Console.WriteLine("i: " + i.ToString("00") + ", byte: " + GetByte(i, dt).ToString ());
//          }
//          UIGraphics.EndImageContext();



            // METHOD 4
            int bitmapBytesPerRow = width * 4;
            IntPtr bitmapData = Marshal.AllocHGlobal (width * 4 * height);

            CGBitmapContext ctxt = new CGBitmapContext (bitmapData, width, height, cg.BitsPerComponent, bitmapBytesPerRow, cg.ColorSpace, CGImageAlphaInfo.PremultipliedLast);

            RectangleF rect = new RectangleF (0.0f, 0.0f, width, height);
            ctxt.DrawImage (rect, _CarrierImage.CGImage); 
            IntPtr dt = ctxt.Data;

            Console.WriteLine ("R: " + GetByte (0, dt).ToString ());
            Console.WriteLine ("G: " + GetByte (1, dt).ToString ());
            Console.WriteLine ("B: " + GetByte (2, dt).ToString ());
            Console.WriteLine ("A: " + GetByte (3, dt).ToString ());

            return true;
        }

        unsafe byte GetByte (int offset, IntPtr buffer)
        {
            byte* bufferAsBytes = (byte*)buffer;
            return bufferAsBytes [offset];
        }

    }
}

适用于iOS的Monotouch中的透明PNG

0 个答案: