In the latest episode of Fairlight TV, Trident, a seasoned C64 demo coder, shared insights into his highly efficient coding techniques at Fjälldata 2025. Over the past year, he has produced more than 300 demo parts, demonstrating a streamlined approach that transforms the traditionally time-consuming process into an efficient and enjoyable endeavor. His efficiency is attributed to two key techniques designed to simplify the complexities of C64 programming.
First, Trident addresses the notorious challenge of managing interrupt request (IRQ) handlers. In conventional C64 demo coding, IRQs can quickly become an unmanageable web of code, with each requiring a unique name and address. Inserting a new IRQ between existing ones often necessitates extensive modifications, making the process cumbersome.
Trident’s innovative solution is the use of “Anonymous IRQ Handlers.” Instead of naming each IRQ individually, he employs a single, streamlined handler that utilizes a macro called “irq wait,” which takes a raster line number as input. This macro sets up the next interrupt to point to the line of code immediately following it, creating a linear, sequential flow. This approach simplifies code structure, making it easier to modify and expand without adding overhead.
Trident’s second technique is “Proto Threads,” designed to manage sequencing actions over time. Traditionally, implementing timed events such as displaying a logo after two seconds, followed by text and a scrolling effect, requires complex state machines, timer-based triggers, or custom script engines. These methods often introduce significant complexity and maintenance challenges.
Trident’s Proto Threads offer a streamlined alternative. Inspired by his PhD research on lightweight threading, he adapted the concept for the C64. Proto Threads function as special subroutines that remember their execution position and resume where they left off using an indirect jump technique. This minimizes overhead while allowing for intuitive, script-like code: “wait for two seconds, show logo, wait for one second, show text, wait for four seconds, start scroll.” This approach simplifies the development of time-based effects, making them more manageable and flexible.
These two techniques—Anonymous IRQ Handlers and Proto Threads—are not about complex algorithms or obscure methods but about optimizing and simplifying the coding process. Trident’s approach makes C64 demo coding more accessible and efficient, proving that sometimes the simplest solutions are the most effective.
