浅谈Winform控件开发（一）：使用GDI+美化基础窗口

写在前面：
本系列第一篇内容将仅包含对于winform基础窗口也就是system.windows.forms.form的美化，后续将对一些常用控件如button、combobox、checkbox、textbox等进行修改，并提供一些其他如loading遮罩层等常见控件。
对于基础窗口的美化，首要的任务就是先把基础标题栏干掉。这个过程中会涉及一些windows消息机制。

首先，我们新建一个类xform，派生自system.windows.forms.form。

1 /// <summary>
2 /// 表示组成应用程序的用户界面的窗口或对话框。
3 /// </summary>
4 [toolboxitem(false)]
5 public class xform : form
6 ...

随后，我们定义一些常量

 1 /// <summary>
 2 /// 标题栏高度
 3 /// </summary>
 4 public const int titlebarheight = 30;
 5 
 6 // 边框宽度
 7 private const int borderwidth = 4;
 8 // 标题栏图标大小
 9 private const int iconsize = 16;
10 // 标题栏按钮大小
11 private const int buttonwidth = 30;
12 private const int buttonheight = 30;

覆盖基类属性formborderstyle使base.formborderstyle保持none，覆盖基类属性padding返回或设置正确的内边距

 1 /// <summary>
 2 /// 获取或设置窗体的边框样式。
 3 /// </summary>
 4 [browsable(true)]
 5 [category("appearance")]
 6 [description("获取或设置窗体的边框样式。")]
 7 [defaultvalue(formborderstyle.sizable)]
 8 public new formborderstyle formborderstyle
 9 {
10     get => _formborderstyle;
11     set
12     {
13         _formborderstyle = value;
14         updatestyles();
15         drawtitlebar();
16     }
17 }
18 
19 /// <summary>
20 /// 获取或设置窗体的内边距。
21 /// </summary>
22 [browsable(true)]
23 [category("appearance")]
24 [description("获取或设置窗体的内边距。")]
25 public new padding padding
26 {
27     get => new padding(base.padding.left, base.padding.top, base.padding.right, base.padding.bottom - titlebarheight);
28     set => base.padding = new padding(value.left, value.top, value.right, value.bottom + titlebarheight);
29 }

※最后一步也是最关键的一步：重新定义窗口客户区边界。重写wndproc并处理wm_nccalcsize消息。

 1 protected override void wndproc(ref message m)
 2 {
 3     switch (m.msg)
 4     {
 5             case wm_nccalcsize:
 6             {
 7                 // 自定义客户区
 8                 if (m.wparam != intptr.zero && _formborderstyle != formborderstyle.none)
 9                 {
10                     nccalcsize_params @params = (nccalcsize_params)
11                         marshal.ptrtostructure(m.lparam, typeof(nccalcsize_params));
12                     @params.rgrc[0].top += titlebarheight;
13                     @params.rgrc[0].bottom += titlebarheight;
14                     marshal.structuretoptr(@params, m.lparam, false);
15                     m.result = (intptr)(wvr_aligntop | wvr_alignbottom | wvr_redraw);
16                 }
17 
18                 base.wndproc(ref m);
19                 break;
20             }
21 ……

相关常量以及p/invoke相关方法已在我的库中定义，详见msdn，也可从查询。
同样在wndproc中处理wm_ncpaint消息

1 case wm_ncpaint:
2 {
3     drawtitlebar();
4     m.result = (intptr)1;
5     break;
6 }

drawtitlebar()方法定义如下：

 1 /// <summary>
 2 /// 绘制标题栏
 3 /// </summary>
 4 private void drawtitlebar()
 5 {
 6     if (_formborderstyle == formborderstyle.none)
 7         return;
 8 
 9     drawtitlebackgroundtexticon();
10     createbuttonimages();
11     drawtitlebuttons();
12 }

首先使用线性渐变画刷绘制标题栏背景、图标、标题文字：

 1 /// <summary>
 2 /// 绘制标题栏背景、文字、图标
 3 /// </summary>
 4 private void drawtitlebackgroundtexticon()
 5 {
 6     intptr hdc = getwindowdc(handle);
 7     graphics g = graphics.fromhdc(hdc);
 8 
 9     // 标题栏背景
10     using (brush brstitlebar = new lineargradientbrush(titlebarrectangle,
11         _titlebarstartcolor, _titlebarendcolor, lineargradientmode.horizontal))
12         g.fillrectangle(brstitlebar, titlebarrectangle);
13 
14     // 标题栏图标
15     if (showicon)
16         g.drawicon(icon, new rectangle(
17             borderwidth, titlebarrectangle.top + (titlebarrectangle.height - iconsize) / 2,
18             iconsize, iconsize));
19 
20     // 标题文本
21     const int txtx = borderwidth + iconsize;
22     sizef sztext = g.measurestring(text, systemfonts.captionfont, width, stringformat.genericdefault);
23     using brush brstext = new solidbrush(_titlebarforecolor);
24     g.drawstring(text,
25         systemfonts.captionfont,
26         brstext,
27         new rectanglef(txtx,
28             titlebarrectangle.top + (titlebarrectangle.bottom - sztext.height) / 2,
29             width - borderwidth * 2,
30             titlebarheight),
31         stringformat.genericdefault);
32 
33     g.dispose();
34     releasedc(handle, hdc);
35 }

随后绘制标题栏按钮，犹豫篇幅限制，在此不多赘述，详见源码中createbuttonimages()与drawtitlebuttons()。

至此，表面工作基本做完了，但这个窗口还不像个窗口，因为最小化、最大化、关闭以及调整窗口大小都不好用。

为什么？因为还有很多工作要做，首先，同样在wndproc中处理wm_nchittest消息，通过m.result指定当前鼠标位置位于标题栏、最小化按钮、最大化按钮、关闭按钮或上下左右边框

 1 case wm_nchittest:
 2     {
 3         base.wndproc(ref m);
 4 
 5         point pt = pointtoclient(new point((int)m.lparam & 0xffff, (int)m.lparam >> 16 & 0xffff));
 6 
 7         _usersizedormoved = true;
 8 
 9         switch (_formborderstyle)
10         {
11             case formborderstyle.none:
12                 break;
13             case formborderstyle.fixedsingle:
14             case formborderstyle.fixed3d:
15             case formborderstyle.fixeddialog:
16             case formborderstyle.fixedtoolwindow:
17                 if (pt.y < 0)
18                 {
19                     _usersizedormoved = false;
20                     m.result = (intptr)htcaption;
21                 }
22 
23                 if (correcttological(closebuttonrectangle).contains(pt))
24                     m.result = (intptr)htclose;
25                 if (correcttological(maximizebuttonrectangle).contains(pt))
26                     m.result = (intptr)htmaxbutton;
27                 if (correcttological(minimizebuttonrectangle).contains(pt))
28                     m.result = (intptr)htminbutton;
29 
30                 break;
31             case formborderstyle.sizable:
32             case formborderstyle.sizabletoolwindow:
33                 if (pt.y < 0)
34                 {
35                     _usersizedormoved = false;
36                     m.result = (intptr)htcaption;
37                 }
38 
39                 if (correcttological(closebuttonrectangle).contains(pt))
40                     m.result = (intptr)htclose;
41                 if (correcttological(maximizebuttonrectangle).contains(pt))
42                     m.result = (intptr)htmaxbutton;
43                 if (correcttological(minimizebuttonrectangle).contains(pt))
44                     m.result = (intptr)htminbutton;
45 
46                 if (windowstate == formwindowstate.maximized)
47                     break;
48 
49                 bool btop = pt.y <= -titlebarheight + borderwidth;
50                 bool bbottom = pt.y >= height - titlebarheight - borderwidth;
51                 bool bleft = pt.x <= borderwidth;
52                 bool bright = pt.x >= width - borderwidth;
53 
54                 if (bleft)
55                 {
56                     _usersizedormoved = true;
57                     if (btop)
58                         m.result = (intptr)httopleft;
59                     else if (bbottom)
60                         m.result = (intptr)htbottomleft;
61                     else
62                         m.result = (intptr)htleft;
63                 }
64                 else if (bright)
65                 {
66                     _usersizedormoved = true;
67                     if (btop)
68                         m.result = (intptr)httopright;
69                     else if (bbottom)
70                         m.result = (intptr)htbottomright;
71                     else
72                         m.result = (intptr)htright;
73                 }
74                 else if (btop)
75                 {
76                     _usersizedormoved = true;
77                     m.result = (intptr)httop;
78                 }
79                 else if (bbottom)
80                 {
81                     _usersizedormoved = true;
82                     m.result = (intptr)htbottom;
83                 }
84                 break;
85             default:
86                 throw new argumentoutofrangeexception();
87         }
88         break;
89     }

随后以同样的方式处理wm_nclbuttondblclk、wm_nclbuttondown、wm_nclbuttonup、wm_ncmousemove等消息，进行标题栏按钮等元素重绘，不多赘述。

现在窗口进行正常的单击、双击、调整尺寸，我们在最后为窗口添加阴影

首先定义一个可以承载32位位图的分层窗口(layered window)来负责主窗口阴影的呈现，详见源码中xformshadow类，此处仅列出用于创建分层窗口的核心代码：

 1 private void updatebmp(bitmap bmp)
 2 {
 3     if (!ishandlecreated) return;
 4 
 5     if (!image.iscanonicalpixelformat(bmp.pixelformat) || !image.isalphapixelformat(bmp.pixelformat))
 6         throw new argumentexception(@"位图格式不正确", nameof(bmp));
 7 
 8     intptr oldbits = intptr.zero;
 9     intptr screendc = getdc(intptr.zero);
10     intptr hbmp = intptr.zero;
11     intptr memdc = createcompatibledc(screendc);
12 
13     try
14     {
15         point formlocation = new point(left, top);
16         size bitmapsize = new size(bmp.width, bmp.height);
17         blendfunction blendfunc = new blendfunction(
18             ac_src_over,
19             0,
20             255,
21             ac_src_alpha);
22 
23         point srcloc = new point(0, 0);
24 
25         hbmp = bmp.gethbitmap(color.fromargb(0));
26         oldbits = selectobject(memdc, hbmp);
27 
28         updatelayeredwindow(
29             handle,
30             screendc,
31             ref formlocation,
32             ref bitmapsize,
33             memdc,
34             ref srcloc,
35             0,
36             ref blendfunc,
37             ulw_alpha);
38     }
39     finally
40     {
41         if (hbmp != intptr.zero)
42         {
43             selectobject(memdc, oldbits);
44             deleteobject(hbmp);
45         }
46 
47         releasedc(intptr.zero, screendc);
48         deletedc(memdc);
49     }
50 }

最后通过路径渐变画刷创建阴影位图，通过位图构建分层窗口，并与主窗口建立父子关系：

 1 /// <summary>
 2 /// 构建阴影
 3 /// </summary>
 4 private void buildshadow()
 5 {
 6     lock (this)
 7     {
 8         _buildingshadow = true;
 9 
10         if (_shadow != null && !_shadow.isdisposed && !_shadow.disposing)
11         {
12             // 解除父子窗口关系
13             setwindowlong(
14                 handle,
15                 gwl_hwndparent,
16                 0);
17 
18             _shadow.dispose();
19         }
20 
21         bitmap bmpbackground = new bitmap(width + borderwidth * 4, height + borderwidth * 4);
22 
23         graphicspath gp = new graphicspath();
24         gp.addrectangle(new rectangle(0, 0, bmpbackground.width, bmpbackground.height));
25 
26         using (graphics g = graphics.fromimage(bmpbackground))
27         using (pathgradientbrush brs = new pathgradientbrush(gp))
28         {
29             g.compositingmode = compositingmode.sourcecopy;
30             g.interpolationmode = interpolationmode.highqualitybicubic;
31             g.pixeloffsetmode = pixeloffsetmode.highquality;
32             g.smoothingmode = smoothingmode.antialias;
33 
34             // 中心颜色
35             brs.centercolor = color.fromargb(100, color.black);
36             // 指定从实际阴影边界到窗口边框边界的渐变
37             brs.focusscales = new pointf(1 - borderwidth * 4f / width, 1 - borderwidth * 4f / height);
38             // 边框环绕颜色
39             brs.surroundcolors = new[] { color.fromargb(0, 0, 0, 0) };
40             // 掏空窗口实际区域
41             gp.addrectangle(new rectangle(borderwidth * 2, borderwidth * 2, width, height));
42             g.fillpath(brs, gp);
43         }
44 
45         gp.dispose();
46 
47         _shadow = new xformshadow(bmpbackground);
48 
49         _buildingshadow = false;
50 
51         alignshadow();
52         _shadow.show();
53 
54         // 设置父子窗口关系
55         setwindowlong(
56             handle,
57             gwl_hwndparent,
58             _shadow.handle.toint32());
59 
60         activate();
61     }//end of lock(this)
62 }

感谢大家能读到这里，代码中如有错误，或存在其它建议，欢迎在评论区或github指正。

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