Crate vga_framebuffer

VGA Frame Buffer for Embedded Microcontrollers

Generates an 800 x 600 @ 60 Hz SVGA signal from a 48 column x 36 row monochrome text buffer. The image has a border.

TODO: Implement smooth scrolling in the vertical direction with an extra text row.

Width = 400 double width pixels => 400 = 8 + (48 x 8) + 8

Height = 600 pixels => 600 = 12 + (36 x 16) + 12

<-------------- 400 px, pixel doubled to 800 px ------------->
+------------------------------------------------------------+
|<--> 8 pixel border     ^                8 pixel border <-->|
|                        | 12 px border                      |
|                        v                                   |
|    +--------------------------------------------------+    |
|    | <--^------ 48 chars x 8 px = 384  px ----------->|    |
|    |    |                                             |    |
|    |    |                                             |    |
|    |    | 36 rows x 16 px = 576 px                    |    |
|    |    |                                             |    |
|    |    |                                             |    |
|    |    v                                             |    |
|    +--------------------------------------------------+    |
|                          ^                                 |
|                          | 12 px border                    |
|                          v                                 |
+------------------------------------------------------------+

Requires pixels to be emitted with a 20 MHz pixel clock (against a nominal 40 MHz pixel clock, in order to acheive the horizontal doubling).

In order to maintain performance, only one font size is supported: 8x16 pixels. But you can substitute your own font if required (e.g. for Teletext support).

There is optional cursor support. Rather than try and check each text cell at render time to see if it is in the cursor position, we swap chars in and out of the text buffer as the cursor moves. It’s a little more expensive, but the cost is at text write time, not at render time (and so it won’t break sync).

See https://github.com/thejpster/monotron for an example.

Modules

freebsd_cp850

freebsd_teletext

Structs

Attr

This structure describes the attributes for a Char. They’re all packed into 8 bits to save RAM.

Col

Describes a vertical column on the screen. Zero is on the left.

FrameBuffer

This structure represents the framebuffer - a 2D array of monochome pixels.

Mode2

Represents Mode2 1-bpp graphics

Point

A point on the screen. The arguments are X (column), Y (row)

Position

Describes a place on the screen. (0, 0) is the top left.

Row

Identifies a horizontal row on the screen. Zero is at the top.

TextRow

Enums

Char

This MS-DOS CodePage 850. It offers a compromise between the box characters of CodePage 437 and the accents of ISO 8859-1 / Latin-1.

Colour

ControlCharMode

How to handle Control Characters

DoubleHeightMode

You can set this on a row to make the text double-height. This was common on the BBC Micro in Mode 7/Teletext mode.

EscapeCharMode

SpecialChar

Special types of character we need to interpret

Constants

HORIZONTAL_OCTETS

How many words in a line (including the border)

LEFT_RIGHT_BORDER_WIDTH

MAX_X

Highest X co-ord

MAX_Y

Highest Y co-ord

TEXT_MAX_COL

Highest X co-ord for text

TEXT_MAX_ROW

Highest Y co-ord for text

TEXT_NUM_COLS

How many characters in a row

TEXT_NUM_ROWS

How many rows of characters on the screen

TOP_BOTTOM_BORDER_HEIGHT

Top/bottom border height

USABLE_COLS

Number of columns in frame buffer

USABLE_HORIZONTAL_OCTETS

How many words in a line (excluding the border)

USABLE_LINES

Number of lines in frame buffer

USABLE_LINES_MODE2

Number of lines in the mode2 frame buffer (which is line-doubled)

Traits

AsciiConsole

Refinement of BaseConsole which supports 8-bit characters. Use this is you are implementing an old-fashioned ASCII console (including extended ASCII, like Code Page 850, or ISO 8859-1).

BaseConsole

Abstraction for our console. We can move the cursor around and write text to it. You should use either UnicodeConsole or AsciiConsole depending on whether you want full Unicode support (&str, char, etc), or just 8-bit characters (&[u8] and u8).

Hardware

Implement this on your microcontroller’s timer object.

UnicodeConsole

Refinement of BaseConsole which supports Unicode characters. Use this is you are implementing a modern console with Unicode support.