Tech Note 04: Using Color Objects and Graphics

Contributed by Adrian Nicolaiev.

NS Basic/Symbian OS uses System Palettes to describe the color scheme of objects. Colors for each object are defined by the palette, rather than in the object itself. Therefore, all the buttons on a screen will share the same color scheme, etc. The information in this Tech Note is fairly low level: an easier way to manipulate colors is to use the ScreenLib, described in Tech Note 13.

In this Tech Note, we will give a short introduction to System Palettes. Then, we will define Color Table and UI Color List with its enum Entries. Finally, we will discuss some Window Functions and UI Color Functions showing how it is possible, using API functions and some tricks, to develop a full color project in NSBasic.

Introduction

System palettes of 1, 2, 4, or 8 bits-per-pixel are supported, as follows:

1-bit: white (0) and black (1)
2-bit: white (0), light gray (1), dark gray (2), and black (3)
4-bit: 16 shades of gray, from white (0) to black (0xF)
8-bit: 216 color "Web-safe" palette, which includes all combinations of red, green, and blue at these levels: 0x00, 0x33, 0x66, 0x99, 0xCC, and 0xFF. Also, it includes gray shades at these levels: 0x22, 0x44, 0x55, 0x77, 0x88, 0xAA, 0xBB, 0xDD, 0xEE. Finally, it includes these extra named HTML colors: 0xC0C0C0 (silver), 0x808080 (gray), 0x800000 (maroon), 0x800080 (purple), 0x008000 (green), and 0x008080 (teal). The remaining 26 entries (indexes 230 through 255) are unspecified and filled with black. (On debug ROMs they are filled with random colors to help developers notice if they use an invalid value.)

Color Table

The color table is a count of the number of entries, followed by an array of RGBColorType colors. An RGBColorType struct holds 8 bits each of red, green, and blue plus an "extra" byte to hold an index value.
A color's index is used in different ways by different software layers. When querying for a color or doing color fitting, the index holds the index of the closest match to the RGB value in the reference color table. When setting a color in a color table, the index can specify which slot the color should occupy. *In some routines, the index is ignored.


Color Palette 8-bit	16 Gray Scale Palette 4-bit

UI Color List

The system builds a UI Color List in addition to the system Color Table. The UI Color List contains the colors used by the various user interface elements. Each UI color is represented by a symbolic color constant.

Do not confuse the UI Color List with the system Color Table. The system color table (or system palette) defines all available colors for the display or draw window, whether they are in use or not. The UI Color List defines the colors used to draw the interface objects.

UI Color Table Entries

The UIColorTableEntries enum declares symbolic color constants for the various UI elements.

Function Index and Quick Reference

UI Color Functions

UIColorGetTableEntryIndex

IndexedColorType
        UIColorGetTableEntryIndex (UIColorTableEntries which)

where which is one of the symbolic color constants in UIColorTableEntries

Return:

Example:

Dim which as Short

        Dim IndexedColor as Short

        which = 11 'UIFieldText, for example.

        which = which * 256

        IndexedColor = SysTrapFunc(932,1,which)

UIColorGetTableEntryRGB

void UIColorGetTableEntryRGB (UIColorTableEntries which,
        RGBColorType *rgbP)

where which is one of the symbolic color constants in UIColorTableEntries and *rgbP is a returned pointer to an RGB color value corresponding to the current color used for the symbolic color.

Return:

Example:

Dim which as Short

        Dim rgbP as String

        which = 10 'UIFieldBackground, for example.

        which = which * 256

        SysTrapSub 933,2,which,rgbP

UIColorSetTableEntry

Err UIColorSetTableEntry (UIColorTableEntries which,
        const RGBColorType *rgbP)

where which is one of the symbolic color constants in UIColorTableEntries and const *rgbP is the RGB value of the color that should be used for the specified UI object defined as which.

Return:

Example:

Dim Err as Short

        Dim which as Short

        Dim constrgbP as String 'You will see why...

        which = constant * 256

Here is where you insert RGB Table values :-)
This was "the tip of the ICEBERG". This was found while working on Window Functions using Indexed colors and converting them back to RGB: RGBColor is a 4-byte value representing:
Index (may be *anything) + Red (byte) + Green (byte) + Blue (byte).
So, an RGB would be, for example, "$" + &h66 + &h33 + &hCC if you are picking color 64 (6633CC) in RGBColorType
constrgbP = "$" + &h66 + &h33 + &hCC
Err = SysTrapFunc(934,2,which,constrgbP)
But, if you wish color index 96 (00FFCC)?
Answer: the system will consider the first 00 (null char) as the end of a string and will take 00FFCC00 as its value. It will become color index 121 :-(
Solution:
Another "tip of the iceberg"... remember: "the index holds the index of the closest match to the RGB value". So, color index 96, for example, could be (01FFCC) :-)
and the system will *convert* to the closest RGB index color: 00FFCC...

Window Functions

WinIndexToRGB

void WinIndexToRGB (IndexedColorType i,
        RGBColorType *rgbP)

where i is a color index value and rgbP is a pointer to an RGB color value corresponding to the index value i.

Return:

Example:

Dim i as Short

        Dim rgbP as Variant

        i = 134 'Indexed color 134

        i = i * 256

        SysTrapSub 927,2,i,rgbP

WinRGBToIndex

Return:

Example

Dim constrgbP as String

        Dim IndexedColor as Short

        constrgbP = "$"
        + &h66 + &h33 +
        &hCC 'For example

        IndexedColor = SysTrapFunc(926,1,constrgbP)

WinSetForeColor

Return:

Example:

Dim ForeIndexedColor as Short

        Dim ForePreviousIndexedColor as Short

        ForeIndexedColor = 96 'For example

        ForeIndexedColor = ForeIndexedColor * 256

        ForePreviousIndexedColor = SysTrapFunc(920,1,ForeIndexedColor)

WinSetBackColor

Return:

Example:

Dim BackIndexedColor as Short

        Dim BackPreviousIndexedColor as Short

        BackIndexedColor = 96 'For example

        BackIndexedColor = BackIndexedColor * 256

        BackPreviousIndexedColor = SysTrapFunc(921,1,BackIndexedColor)

WinSetTextColor

Return:

Example:

Dim textIndexedColor as Short

        Dim textPreviousIndexedColor as Short

        textIndexedColor = 96 'For example

        textIndexedColor = textIndexedColor * 256

        textPreviousIndexedColor = SysTrapFunc(922,1,textIndexedColor)

WinDrawGrayLine

Return:

Nothing.
This routine does not draw in the gray color; it draws with alternating foreground and background pixels

Example:

Dim x1 as Short

        Dim y1 as Short

        Dim x2 as Short

        Dim y2 as Short

        SysTrapSub 532,4,x1,y1,x2,y2

WinDrawPixel

Return:

Example:

WinErasePixel

Return:

Example:

WinInvertPixel

Return:

Example:

WinGetPixel

Return:

Example:

Dim x as Short

        Dim y as Short

        Dim PixelIndexedColor as Short

        PixelIndexedColor = SysTrapFunc(897,2,x,y)

WinEraseLine

Return:

Example:

Dim x1 as Short

        Dim y1 as Short

        Dim x2 as Short

        Dim y2 as Short

        SysTrapSub 533,4,x1,y1,x2,y2

WinInvertLine

Return:

Example:

Dim x1 as Short

        Dim y1 as Short

        Dim x2 as Short

        Dim y2 as Short

        SysTrapSub 534,4,x1,y1,x2,y2

WinScreenLock

Return:

A pointer to the new screen base address.
"Lock" the current screen by switching the UI concept of the screen base address to an area that is not reflected on the display. This routine can be used to "freeze" the display while doing lengthy drawing operations to avoid a flickering effect. Call WinScreenUnlock to unlock the display and cause it to be updated with any changes. The screen must be unlocked as many times as it is locked to actually update the display.

Example:

Dim initMode as Short

        Dim screenAddress as Variant

        initMode = 0 'Copy old screen to new

        screenAddress = SysTrapFunc(928,1,initMode)

WinScreenUnlock

Return:

Nothing.
Unlock the screen and update the display.
The screen must be unlocked as many times as it is locked to actually update the display.

UI Color Functions
`UIColorGetTableEntryIndex`	`IndexedColorType UIColorGetTableEntryIndex (UIColorTableEntries which)`
`UIColorGetTableEntryRGB`	`void UIColorGetTableEntryRGB (UIColorTableEntries which, RGBColorType *rgbP)`
`UIColorSetTableEntry`	`Err UIColorSetTableEntry (UIColorTableEntries which, const RGBColorType *rgbP)`
Window Functions
`WinIndexToRGB`	`void WinIndexToRGB (IndexedColorType i, RGBColorType *rgbP)`
`WinRGBToIndex`	`IndexedColorType WinRGBToIndex (const RGBColorType *rgbP)`
`WinSetForeColor`	`IndexedColorType WinSetForeColor (IndexedColorType foreColor)`
`WinSetBackColor`	`IndexedColorType WinSetBackColor (IndexedColorType backColor)`
`WinSetTextColor`	`IndexedColorType WinSetTextColor (IndexedColorType textColor)`
`WinDrawGrayLine`	`void WinDrawGrayLine (Coord x1, Coord y1, Coord x2, Coord y2)`
`WinDrawPixel`	`void WinDrawPixel (Coord x, Coord y)`
`WinErasePixel`	`void WinErasePixel (Coord x, Coord y)`
`WinInvertPixel`	`void WinInvertPixel (Coord x, Coord y)`
`WinGetPixel`	`IndexedColorType WinGetPixel (Coord x, Coord y)`
`WinEraseLine`	`void WinEraseLine (Coord x1, Coord y1, Coord x2, Coord y2)`
`WinInvertLine`	`void WinInvertLine (Coord x1, Coord y1, Coord x2, Coord y2)`
`WinScreenLock`	`UInt8* WinScreenLock (WinLockInitType initMode)`
`WinScreenUnlock`	`void WinScreenUnlock (void)`