Screen Graphics

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Screen (Graphics)

Opens a graphics mode by mode number, or picks the work and visible pages.

Syntax

-lang fb|fblite dialects:
Screen mode [, [ depth ] [, [ num_pages ] [, [ flags ] [, [ refresh_rate ]]]]]
Screen , [ active_page ] [, [ visible_page ]]
-lang qb dialect:
Screen [ mode ] [, [ colormode ] [, [ active_page ] [, [ visible_page ]]]]

Parameters

• mode
• mode
• depth
• num_pages
• flags
• refresh_rate
• active_page
• visible_page
• colormode

Description

Screen tells the compiler to link the GfxLib and initializes a QB-only, QB-on-GUI or OpenGL graphics mode, depending on the flags setting.

In QB-only modes a dumb window or fullscreen resolution is set, one or more buffers in standard memory are created, console commands are redirected to their graphic versions, a default palette is set and an automatic screen refresh thread is started. QB-like graphics and console statements can be used.

In QB-on-GUI modes one or more buffers in standard memory are created, console commands are redirected to their graphic versions and a default palette is set. QB-like graphics and console statements can be used. It is up to the user to create a window and to refresh it with the contents of the graphics buffers.

In OpenGL modes a dumb window or fullscreen resolution is set, one or more buffers in standard memory are created, and the OS's OpenGL library is initialized. From here only OpenGL commands can be used; QB-like and console commands are forbidden. This allows to initialize OpenGL in a portable way; you can then also use ScreenControl to properly customize the GL pixel format to be used before Screen is called or to retrieve the list of supported OpenGL extensions after a mode has been set, and ScreenGLProc to obtain extension function pointers.

Any buffer that is created in standard memory uses one of three supported internal pixel formats, depending on the desired color depth; see Internal pixel formats for details.

If Screen fails to set the required mode, an "Illegal function call" error is issued and the screen pointer is set to 0. Thus Screen failures can be detected using standard On Error processing or retrieving the screen pointer with ScreenPtr.

Before setting a fullscreen mode the program should check if that mode is available in the graphics card using ScreenList.

mode details

Available modes list:

QB compatibility modes:

Mode nr	Resolution	Emulation	Text	char size	colors on screen
1	320x200	CGA	40X25	8x8	16 background, 1 of four sets foreground
2	640x200	CGA	80x25	8x8	16 colors to 2 attributes
7	320x200	EGA	40x25	8x8	16 colors to 16 attributes
8	640x200	EGA	80x25	8x8	16 colors to 16 attributes
9	640x350	EGA	80x25 0r 80x43	8x14 or 8x8	16 colors to 16 attributes
11	640x480	VGA	80x30 or 80x60	8x16 or 8x8	256K colors to 2 attributes
12	640x480	VGA	80x30 or 80x60	8x16 or 8x8	256K colors to 16 attributes
13	320x200	MCGA	40X25	8X8	256K colors to 256 attributes

(the mode number '0' is dedicated to text mode)

New FreeBASIC modes:

Mode nr	Resolution	Emulation	Text	char size	colors on screen
14	320x240		40x30	8x8	256K colors to 256 attributes or direct color
15	400x300		50x37	8x8	256K colors to 256 attributes or direct color
16	512x384		64x24 or 64x48	8x16 or 8x8	256K colors to 256 attributes or direct color
17	640x400		80x25 or 80x50	8x16 or 8x8	256K colors to 256 attributes or direct color
18	640x480		80x30 or 80x60	8x16 or 8x8	256K colors to 256 attributes or direct color
19	800x600		100x37 or 100x75	8x16 or 8x8	256K colors to 256 attributes or direct color
20	1024x768		128x48 or 128x96	8x16 or 8x8	256K colors to 256 attributes or direct color
21	1280x1024		160x64 or 160x128	8x16 or 8x8	256K colors to 256 attributes or direct color

depth details

For modes 14 and up, the depth parameter changes the color depth to the specified new one; if depth is not specified, these modes run in 8bpp. For modes 13 and below, depth has no effect.

num_pages details

You can request any number of pages for any video mode; if you omit the parameter, only the visible page (number 0) will be available. A page is either the visible screen or an offscreen buffer, you can show a page while working on another one; see the ScreenSet statement for details. All pages are created in standard memory, the video card memory is never used for video buffering.

flags details:

(documented at the page ScreenRes)

Other details

While in windowed mode, clicking on the window close button will add a keypress of (Chr(255) & "k") to the Inkey buffer. Clicking on the Maximize window button will switch to fullscreen mode if possible. A successful Screen call sets currently visible and working pages both to page number 0, resets the palette to the specified mode one (see Default palettes), resets the clipping region to the size of the screen, disables custom coordinates mappings, moves the graphics cursor to the center of the screen, moves the text cursor to the top-left corner of the screen (but never visible on any graphics screen), and sets foreground and background colors to bright white and black respectively.

Note on using Screen 0 (text mode only)

The default BASIC screen mode (Screen 0) is text based.
Screen 0 closes any graphics window, but also clears the console window if it exists.
Screen 0, , , GFX_SCREEN_EXIT (with GFX_SCREEN_EXIT=&h80000000) also closes any graphics window, but does not clear the console window if it exists (previous text is preserved).

Remarks

Platform Differences

• In DOS, Windowing and OpenGL related switches are not available, and other issues, see GfxLib overview

Dialect Differences

• In the -lang fb and -lang fblite dialects, the usage is:

Screen mode [, [depth] [, [num_pages] [, [flags] [, [refresh_rate]]]]]
or:
Screen , [active_page] [, [visible_page]]]

• In the -lang qb dialect, the usage is:

Screen [mode] [, [colormode] [, [active_page] [, [visible_page]]]]

Differences from QB

• None in the -lang qb dialect. In QB the syntax was Screen mode,colormode,active_page,visible_page. Of those parameters FreeBASIC supports only mode and redefines the rest. The use of Screen , , apage,vpage to swap screen pages is only available in the -lang qb dialect.
  ScreenSet should be used in the -lang fb and -lang fblite dialects.

See also

• Screen (Console)
• ScreenRes More flexible alternative to Screen
• ScreenList Check display modes available for FB GfxLib to use
• ScreenControl Select driver and more
• ScreenLock
• ScreenUnlock
• ScreenPtr Semi-low level access
• ScreenSet
• ScreenCopy
• ScreenInfo
• ScreenGLProc

Examples

' Sets screen mode 13 (320*200, 8bpp)

Screen 13

Print "Screen mode 13 set"

Sleep

#include "fbgfx.bi"

#if __FB_LANG__ = "fb"

Using FB '' Screen mode flags are in the FB namespace in lang FB

#endif

' Sets screen mode 18 (640*480) with 32bpp color depth and 4 pages, in windowed mode; switching disabled

Screen 18, 32, 4, (GFX_WINDOWED Or GFX_NO_SWITCH)

' Check to make sure Screen was opened successfully

If ScreenPtr = 0 Then

    Print "Error setting video mode!"

    End

End If

Print "Successfully set video mode"

Sleep

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Category: Screen Functions
Kind: keyword

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Reproduced from the FreeBASIC Wiki Manual under the GNU Free Documentation License 1.3 — with no Invariant Sections, no Front-Cover Texts and no Back-Cover Texts. Copyright © the FreeBASIC project and wiki contributors. See License.