All these tests can be found at teletext_test.c along with descriptions for each case tested. Examples include single/double height mode with or without neighbors, various hold graphics cases to test that hold mode works correctly and it caches the correct block graphic. The tests evaluate various switching cases and edge cases using assert.h. Every unit includes tests, for example the Tokenizer, the Sixels functionality and the Translator logic.
#TELETEXT MACHINE CODE#
The code is clearly separated into units that can be tested and evaluated independently. Position, line) along with other information, so results can be evaluated results without enabling SDL. Run VALGRIND and GDB to check for memory leaks and errors.Įach token and each Teletext “Pixel” has it’s own debug info( ex. Tests are also include for details like cached block graphics. Run the tests in the /testing folder after making changes to the code.
Any other graphics libraries can be implemented.Īttention: Do not rely on visual evaluation. Clear boundaries are kept between the main teletext functionality and the renderer. The renderer takes as an input a Teletext structure and draws it on the screen. Each token produces an output depending on the current state of the translator and if it’s a control code it defines the next state. The translator is implemented as a simple State Machine. It takes a TokenStream as an input and returns a Teletext structure. Translator: It’s where the most work happens. Then it produces a TokenStream.ĭecoder: Consists of a set of functions that decode the control codes and return teletext modes, colors etc. Tokenizer: Takes as input a Teletext file, identifies valid tokens and categorizes them in basic types. This project, inspired by such teletext systems, will allow a 40 × 25 (1000) character file to be rendered to the screen, using similar control codes. Similar system was implemented on the BBC microcomputer, known as Mode 7. This system was trialled first by the BBC in a system that eventually became known as “Ceefax” and then on other independant British terrestrial stations as “Oracle”.
The aim was to provide up-to-date news and weather information via a television set. In the early 1970s, Phillips Labs began work on transmitting digital information across the television network. Implementation of the teletext rendering system in C.
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