SCREEN - QB64 Wiki

SCREEN

From QB64 Wiki

Jump to: navigation, search

Contents

The SCREEN statement sets the video display mode and size of the program window's workspace.


Syntax

SCREEN {mode%|imagehandle&} [, , active_page, visual_page]


Parameters

  • The SCREEN mode INTEGER values available today are 0 to 2 and 7 to 13 listed below.
  • QB64 can use a LONG _NEWIMAGE page or _LOADIMAGE file image handle value instead.
  • The empty comma disables color when any value is used. DO NOT USE! Include the comma ONLY when using page flipping.
  • If the SCREEN mode supports pages, the active page is the page to be worked on while visual page is the one displayed.


Usage:

  • No SCREEN statement in a program defaults to SCREEN 0 text ONLY mode.
  • A SCREEN statement that changes screen modes also clears the screen like CLS. Nothing on the screen is retained.
  • Some screen mode text sizes are adjustable with WIDTH and all QB64 screens support PCOPY and page flipping.

LEGACY SCREEN MODES AT A GLANCE Screen Text Graphics Colors Video Text Default Mode Rows Columns Width Height Attrib. BPP Pages Block QB64 Font 0 25/43/50 80/40 No graphics 16/16 DAC 4 0-7 ----- _FONT 16 1 25 40 320 200 16/4 BG 4 none 8 X 8 _FONT 8 2 25 80 640 200 2/mono 1 none 8 X 8 _FONT 8 ................................................................................. 7 25 40 320 200 16/16 DAC 4 0-7 8 X 8 _FONT 8 8 25 80 640 200 16/16 4 0-3 8 X 8 _FONT 8 9 25 80 640 350 16/64 DAC 4 0-1 8 X 14 _FONT 14 10 25 80 640 350 4/2 GScale 2 none 8 X 14 _FONT 14 11 30/60 80 640 480 2/mono 1 none 8 X 16 _FONT 16 12 30/60 80 640 480 16/262K 4 none 8 X 16 _FONT 16 13 25 40 320 200 256/65K 8 none 8 X 8 _FONT 8 QB64 allows video paging and PCOPY in ALL screen modes!

QB64 Custom Screen Modes
QB64

==Syntax==  

SCREEN imagehandle& [, , active_page, visual_page]
SCREEN _NEWIMAGE(wide&, high&[, {mode|256|32}]) [, , active_page, visual_page]
SCREEN _LOADIMAGE(file$[, {mode|256|32}]) [, , active_page, visual_page]


  • Custom screen modes can be created using a _NEWIMAGE or _LOADIMAGE function imagehandle return value.
  • QB64 screen modes 0 to 2 and 7 to 13 can be emulated with the same color depth and text block size and different dimensions.
  • _NEWIMAGE screens can be any set size. A screen mode can be emulated or 256 or 32 bit colors can be designated.
  • The _LOADIMAGE screen size will be the size of the image loaded. Can designate a mode or 256 or 32 bit colors.
  • QB64 allows page flipping or a PCOPY in ANY SCREEN mode. _DISPLAY can also be used to reduce flickering in animations.
  • All SCREEN modes are Windows in QB64. Use _FULLSCREEN to set the window area to full screen.
  • _SCREENMOVE can position a window or the _MIDDLE option can center it on the desktop.

(Return to Table of Contents)

Legacy Screen Modes

  • SCREEN 0 (default mode) is a text only screen mode. 64 (VGA) colors with hi-intensity(blinking) colors 16 to 31. (DAC attrib 6, 8 to 15). 8 Background colors intensities only(0 - 7). No graphics are possible! Normally runs in a window. ALT-Enter switches from a window to fullscreen. To automatically run in Qbasic fullscreen, use another Screen mode before using SCREEN 0. Can use PCOPY with video pages 0 to 7. Text is 25, 43 or 50 rows by 40 or 80 columns. Default is 25 by 80. See WIDTH.
Note: Use OUT or _PALETTECOLOR to create higher intensity color backgrounds than COLOR , 7.
All other available SCREEN modes can use text and graphics and are fullscreen in Qbasic ONLY.
  • SCREEN 1 has 4 background color attributes. 0 = black, 1 = blue, 2 = green, 3 = grey. White foreground only. Text is 25 by 40. White graphics is 320 by 200.
  • SCREEN 2 is monochrome with black background and white foreground. Text is 25 by 80. White graphics 640 by 200.          NO COLOR keyword allowed.
  • SCREEN 3 to 6 are no longer supported on most computers! Using them will cause a video error!
  • SCREEN 7 has 16 color attributes (DAC attrib. 8 to 15) with background colors. Text 25 rows by 40 columns. Graphics 320 columns by 200 rows. Video pages 0 to 7 for flipping or PCOPY.
  • SCREEN 8 has 16 color attributes with background. Text is 25 by 80. Graphics is 640 by 200. Video pages 0 to 3.
  • SCREEN 9 has 64 DAC color hues for (DAC attrib. 6, 8 to 15) with background colors. Text is 25 by 80. Graphics is 640 by 350. Video pages 0 and 1 for flipping or PCOPY.
  • SCREEN 10 has 4 gray scale color attributes with black background. 1 = normal white, 2 = blinking white and 3 = bright white. Text is 25 by 80. Graphics is 640 by 350.
  • SCREEN 11 is monochrome with black background and white foreground. Text is 30 or 60 by 80 columns(see WIDTH). White graphics is 640 by 480. NO COLOR keyword allowed.
  • SCREEN 12 has 16 color attributes, black background. 256K possible color hues. Text is 30 or 60 by 80 columns(see WIDTH). Graphics 640 by 480.
  • SCREEN 13 has 256 color attributes, black background. 256K possible color hues. Text is 25 by 40. Graphics is 320 by 200.
  • SCREEN _NEWIMAGE(wide&, deep&, mode%) can imitate any size screen mode or use 32 bit or 256 color modes in QB64.
  • SCREEN _LOADIMAGE(imagehandle&, colors) can load a program screen of an image file handle in QB64 using 256 or 32 bit.
QB64 can use page flipping with any number of pages in any screen mode!

(Return to Table of Contents)

Text and Graphics

Text Coordinates:
  • Are a minimum of 1 and the values given above are the maximums. LOCATE 1, 1 is the top left SCREEN text position.
  • Text characters occupy a certain sized pixel box adjusted by WIDTH in some screen modes.
  • Text PRINT cursor positions can be read by CSRLIN and POS(0) to LOCATE text PRINTs.
  • The SCREEN (function) can be used to read the ASCII character code or color of text in SCREEN 0 only.
  • VIEW PRINT can be used to designate a text view port area.
  • In QB64 the _WIDTH and _HEIGHT functions will return the text dimensions in SCREEN 0 only.


Graphic Coordinates:
  • The minimum on screen graphics pixel coordinates are 0 for columns and rows in the top left corner.
  • Maximum pixel coordinates are one less than the maximum dimensions above because the pixel count starts at 0.
  • Graphic objects such as PSET, PRESET, LINE, CIRCLE and DRAW can be placed partially off of the screen.
  • GET and PUT screen image operations MUST be located completely on the screen in Qbasic!
  • VIEW can be used to designate a graphic view port area of the screen.
  • WINDOW can be used to set the graphics SCREEN coordinates to almost any size needed. Use the SCREEN option for normal row coordinate values. Row coordinates are Cartesian(decrease in value going down the screen) otherwise.
  • In QB64 the _WIDTH and _HEIGHT functions will return the graphic pixel dimensions in SCREENs other than 0.


QB64 Screen Statements and Functions:
  • For file image screens that adopt the image dimensions and image color settings use: _LOADIMAGE
  • To create custom sized screen modes or pages and 256 or 32 bit colors use: _NEWIMAGE
  • _PUTIMAGE can stretch or reduce the size of images to fit the SCREEN size.
  • PUT can use _CLIP to set objects partially off screen. GET can read objects off screen as a color in QB64 ONLY.
  • A _DISPLAY statement can be used to only display an image after changes instead of using page flipping or PCOPY.
  • The current desktop screen resolution can be found using the _SCREENIMAGE handle value with _WIDTH and _HEIGHT.
  • NOTE: Default 32 bit backgrounds are clear black or _RGBA(0, 0, 0, 0)! Use CLS to make the black opaque!

(Return to Table of Contents)

Examples

Example 1: Shows an example of each legacy screen mode available to Qbasic and QB64.

SCREEN 0 PRINT "This is SCREEN 0 - only text is allowed!" FOR S = 1 TO 13 IF S < 3 OR S > 6 THEN DO: SLEEP: LOOP UNTIL INKEY$ <> "" SCREEN S PRINT "This is SCREEN"; S; " - can use text and graphics!" IF S = 2 OR S = 11 THEN PRINT "Monochrome - no COLOR statements!" IF S = 10 THEN COLOR 2: PRINT "This SCREEN has only 4 colors. Black and 3 white: 2 blinks. CIRCLE (100,100), 50, 2 ELSE : CIRCLE (100,100), 100, S END IF END IF NEXT SLEEP SYSTEM

This is SCREEN 0 - only text is allowed!

Displays each SCREEN mode one at a time with a CIRCLE (except for SCREEN 0)


Example 2: Making ANY QB64 legacy screen mode larger using a SUB that easily converts PRINT to _PRINTSTRING.

Scr13& = _NEWIMAGE(320, 200, 13) 'this is the old SCREEN 13 image page to set the image Big13& = _NEWIMAGE(640, 480, 256) 'use 4 X 3 aspect ratio that Qbasic used when full screen SCREEN Big13& _DEST Scr13& image1& = _LOADIMAGE("Howie.BMP", 256) 'see the download link below for 2 image files image2& = _LOADIMAGE("Howie2.BMP", 256) _PUTIMAGE (10, 20), image1&, Scr13& _PUTIMAGE (160, 20), image2&, Scr13& _COPYPALETTE image1&, Scr13& COLOR 151: LOCATE 2, 4: PRINTS "Screen 13 Height Reduction to 83%" LOCATE 22, 22: PRINTS CHR$(24) + " 4 X 3 Proportion" 'use concatenation LOCATE 24, 21: PRINTS CHR$(27) + " Stretched at 100%" 'instead of a semicolon! _COPYPALETTE Scr13&, Big13& 'required when imported image colors are used _PUTIMAGE , Scr13&, Big13& 'stretches the screen to double the size K$ = INPUT$(1) END SUB PRINTS (Text$) row% = (CSRLIN - 1) * _FONTHEIGHT 'finds current screen page text or font row height col% = (POS(0) - 1) * _PRINTWIDTH("W") 'finds current page text or font column width _PRINTSTRING (col%, row%), Text$ END SUB

Code by Ted Weissgerber
Explanation: The procedure above creates a larger version of a SCREEN 13 window by stretching it with _PUTIMAGE. It cannot stretch PRINTed text so _PRINTSTRING must be used instead. LOCATE sets the PRINT cursor position for CSRLIN and POS(0) to read. The SUB then converts the coordinates to graphical ones. Then change PRINT to PRINTS using the Search Menu.
Download of Example 2 Bitmap images


You can easily change PRINT to the PRINTS sub-procedure name in your code using the IDE Search Menu Change option.

(Return to Table of Contents)

References

See Examples:

  • SAVEIMAGE (QB64 Image to Bitmap SUB by Galleon)
  • ScreenMode (Member function to find current Screen mode)


See also



Navigation:
Go to Keyword Reference - Alphabetical
Go to Keyword Reference - By usage
Go to Main WIKI Page
Personal tools