Every device context has attributes such as color, font, pen, and palette. GDI32.DLL provides access functions for reading and modifying these attributes. In Visual Basic, canvas objects have properties. Table 7-2 shows how to work with these attributes by means of device contexts in Windows and canvas objects in Visual Basic.
For the most part, you can stick with the Basic Way for reading and modifying attributes. Canvas properties don’t always match up one to one, but they’re usually more convenient. In fact, about the only common task I’ve found that you can’t do with Visual Basic is use a brush (FillStyle) that consists of a bitmap. (After reading “The Windows Way of Painting,” page 390, you should be able to figure that out for yourself.)
Figure 7-2. The ICanvas interface hierarchy.
| Picture- | Form | Printer | Box | Image | Shape | Line | Screen |
| Properties | |||||||
| hDC | x | x | x | ||||
| Picture | x | x | x | ||||
| Image | x | x | |||||
| MouseIcon, MousePointer | x | x | x | x | |||
| Font | x | x | x | ||||
| AutoRedraw | x | x | |||||
| BackColor | x | x | x | ||||
| ForeColor | x | x | x | ||||
| FillColor | x | x | x | x | |||
| DrawMode | x | x | x | x | x | ||
| DrawStyle, DrawWidth | x | x | x | ||||
| FillStyle | x | x | x | x | |||
| CurrentX, CurrentY | x | x | x | ||||
| Width, Height | x | x | x | x | x | x | |
| Left, Top | x | x | x | x | |||
| Scale properties | x | x | x | ||||
| TwipsPerPixelX, | |||||||
| TwipsPerPixelY | x | x | |||||
| Methods | |||||||
| Line, Circle, PSet | x | x | x | ||||
| Point | x | x | |||||
| Cls | x | x | |||||
| x | x | x | |||||
| TextWidth, TextHeight | x | x | x | ||||
| ScaleX, ScaleY | x | x | x | ||||
| PaintPicture | x | x | x |
Table 7-1. Properties and methods of canvas objects.
| Attribute | Windows Way | Basic Way |
| Background color | GetBkColor and SetBkColor | BackColor |
| Background mode | GetBkMode and SetBkMode | FontTransparent |
| Text color | GetTextColor and SetTextColor | ForeColor |
| Color palette | CreatePalette, SelectPalette, and other palette functions | Palette and PaletteMode.properties |
| Brush | Brush creation functions and SelectObject |
FillColor and FillStyle. (but no way to use bitmap brush) |
| Pen | Pen creation functions and SelectObject | DrawStyle and DrawWidth Color parameter of Line and Circle methods |
| Pen color | Pen definition set by Pen creation functions | |
| Pen position | GetCurrentPosition, LineTo, and MoveTo functions | Line method with Step, CurrentX, CurrentY |
| Drawing mode | SetROP2 | DrawMode |
| Font | Font creation functions and SelectObject | Font object |
| Mouse pointer | SelectObject, CreateCursor, and other cursor functions | MousePointer and MouseIcon |
| Clip and redraw state | Various functions related to repainting, managing regions, and clipping | ClipControls, AutoRedraw, and AutoSize |
| Scale | SetMapMode | ScaleMode |
| Window extent and origin | GetWindowExtEx, SetWindowExtEx, GetWindowOrgEx, and SetWindowOrgEx | ScaleLeft, ScaleTop, ScaleWidth, and ScaleHeight |
| Screen capabilities | GetDeviceCaps | Screen object |
Table 7-2. Graphics properties in Windows and in Visual Basic.