draw image

转换的代码应该是平台无关的。Draw里只需要很少的改动。

runtime/datatypes/image.reds 里增加一个函数：
```
any-resize: func [
    ;-- 4 points resize (also support 3 points)
    src         [red-image!]
    dst         [red-image!]
    crop1       [red-pair!]
    start       [red-pair!]     ;-- first point
    end         [red-pair!]     ;-- end point
    /local
        h       [integer!]
        buf     [int-ptr!]
        new-buf [int-ptr!]
][
    h: 0
    buf: acquire-buffer src :h
    
    ; 做转换,结果保存再new-buf里
    
    release-buffer src :h no

    OS-image/load-binary new-buf len
]
```

Draw.reds里面：
```
OS-draw-image: func [
    dc          [draw-ctx!]
    image       [red-image!]
    start       [red-pair!]
    end         [red-pair!]
    key-color   [red-tuple!]
    border?     [logic!]
    crop1       [red-pair!]
    pattern     [red-word!]
    /local
        img     [integer!]
        sub-img [integer!]
        x       [integer!]
        y       [integer!]
        width   [integer!]
        height  [integer!]
        w       [float32!]
        h       [float32!]
        ww      [float32!]
        crop2   [red-pair!]
        trans-img [red-image! value]
][
    either null? start [x: 0 y: 0][x: start/x y: start/y]
    case [
        start = end [
            width:  IMAGE_WIDTH(image/size)
            height: IMAGE_HEIGHT(image/size)
        ]
        start + 1 = end [                   ;-- two control points
            width: end/x - x
            height: end/y - y
        ]
        any [start + 2 = end start + 3 = end][      ;-- 三/四个点的情况。
            image/any-resize image trans-img crop1 start end
            image: trans-img
            crop1: null         ;-- any-resize already handled crop
        ]
        true [0]
    ]

    img: OS-image/to-cgimage image
    if crop1 <> null [
        crop2: crop1 + 1
        w: as float32! crop2/x
        h: as float32! crop2/y
        ww: w / h * (as float32! height)
        width: as-integer ww
        sub-img: CGImageCreateWithImageInRect
            img
            as float32! crop1/x
            as float32! crop1/y
            w
            h
        img: sub-img
    ]

    CG-draw-image dc/raw img x y width height
    if crop1 <> null [CGImageRelease img]
]
```