Show phrases on VGA displays easily and fast (using a framebuffer).
For my project Mastermind, I was using a framebuffer to render scene to a VGA display; at a certain point, I had to display many phrases in game. I discovered this fantastic library, but there was a problem: it didn't adapt very well with how I was writing the scene to the framebuffer; moreover, there was another problem regarding displaying more than one phrase: following this library, I had to instantiate many times a module called pixel_on_text (see library's link to check it out). So, I decided to take this library and refactor it to adapt to my needs: I'm now putting this here as I hope it can helps another developer speed up development.
This project is based on two files: font_rom and text_controller. See next sections to find out how they work.
It's a module containing all the data of characters from ASCII 0 - 127. Basically, it is a long array containing all the characters. Each character contains 8 * 16 pixels. There's also a process returning a row of a character based on a input address (description taken from Derek Wang's repository). This file remained unchanged, I put it here for the sake of completeness.
This is the main module: its logic remains unchanged from Derek Wang's one, I just added some more stuff to make it adapt to every project. Apart from CLOCK and RESET_N signals, that I will take for granted, there are four signals that I will explain:
- CHOSEN_TEXT: it's an input signal that will tell this module which one, of the many phrases you need to show to the display, you need to show now. It's associated with a message type, that is defined like this
type message is (TEXT1, TEXT2, TEXT3, TEXT4);: you need to put this definition in a module, I will tell you after how I suggest you to do it - NEXT_BIT: it's an input signal that will tell this module to go to the next bit of the phrase. If it corresponds to a 1 in the font_rom, PIXEL will become 1 at the end of the process, otherwise, it will stay at 0
- NEXT_LINE: like with NEXT_BIT, but this signal tell this module when to go to the next line
- PIXEL: it will tell you when you need to write to the current coordinates of the framebuffer
Check my project linked before, to see an example of how I implemented it.
I suggest you to create a package, in which you define all your string constants (all your phrases that will need to be displayed on screen sooner or later) and put the message type definition (you can find it in the previous section), that is basically a list of labels for your phrases. Then, you also need to put this other type definition type codes is array(natural range<>) of integer; (it's a dependency for text_controller). Finally, you need to add this row char_codes(n) <= character'pos(TEXT_NAME(char_position)); many times: one for each phrase you need to display; you only need to change n and TEXT_NAME: n stands for the integer associated to the phrase (you define it implicitly when you declare labels for your phrases in the message type, because message is an enum) and TEXT_NAME stands for the label you assigned to the phrase at position n.
You can find a simple text_package in this repo with the message and codes types definition, you can start with that: you only need to modify the message type and add your strings to be displayed.
Text Controller is published under Apache License 2.0. Special thanks to Derek Wang, for his VGA-Text-Generator.
Copyright (©) Davide Di Donato 2018