GDI Improvements: Béziers, Paths, Transforms, Device-Independent Color

GDI, the drawing API for Windows Versions 3.0 and 3.1, provides a useful device-independent drawing set for applications. As output devices have become more sophisticated, so have drawing needs; hence GDI has been improved.

Some Windows applications for Versions 3.0 and 3.1 have needed to implement high-level graphics functions using the low-level drawing primitives of the Windows environment. Although this capability has provided application vendors flexibility in extending the Windows GDI, it has not allowed them to take seamless advantage of advances in printer and display technology. Application developers have had to code their own algorithms for displaying graphics such as Bézier curves and paths. With the Windows 32-Bit API, developers can call new high-level graphics features that will take advantage of the built-in drawing capabilities in advanced output hardware. Under Windows 32, displaying Bézier curves can be handled by the graphics engine or by output devices that have implemented Bézier optimizations.

The Windows 32 GDI is a complete and general-purpose drawing package. Bézier curves are a general-purpose curve primitive from which a straight line can also be derived. This function combined with the PolyBézier functionality makes it possible to draw any combination of continuous lines and curves.

Windows 32 adds a Path API. A BeginPath EndPath sequence “closes” the sequence of drawing primitives between Begin and End. Thus, a BeginPath, PolyPolyBézier, EndPath sequence makes it possible to draw an arbitrary number of different filled shapes.

The Windows 32 transform API maps the virtual two-dimensional surface on which you draw to the two-dimensional output surface. This API, combined with the TrueType font technology first available with Windows Version 3.1, makes it possible to draw truly device-independent graphics that the system can map to the display surface, including the rotation of bitmaps, fonts, and metafiles.

Windows 32 will also provide a device-independent color model. Computer monitors and color printers use different technology to render colors. Additive mixing is used by computer monitors (RGB or Red, Green, Blue), while subtractive mixing (CYMK or Cyan, Yellow, Magenta, Black) is used by color printers. Without device-independent color, the different approach used by monitors and printers can result in mismatched colors.