Trying to build a New kind of terminal emulator for the modern age

post, Jan 26, 2023 on Mitja Felicijan's blog

Over the past few weeks, I have been really thinking about terminal emulators, +how we interact with computers, the separation of text-based programs and GUI +ones. To be perfectly honest, I got pissed off one evening when I was cleaning +up files on my computer. Normally, I go into console and do ncdu and check +where the junk is. Then I start deleting stuff. Without any discrimination, +usually. But when it comes to screenshots, I have learned that it's good to keep +them somewhere near if I need to refer to something that I was doing. I am an +avid screenshot taker. So at that point I checked Pictures folder and also did a +basic search find . -type f -name "*.jpg" for all the JPEG files in my home +directory and immediately got pissed off. Why can’t I see thumbnails in my +terminal? I know why, but why in the year of 2022 this is still a problem. I am +used to traversing my disk via terminal. I am faster, and I am more comfortable +this way. But when it comes to visualization, I then need to revert to GUI +applications and again find the same file to see it. I know that programs like +feh and sxiv are available, but I would just like to see the preview. Like +Jupyter notebook or something similar. Just having it +inline. Part of a result.

It also didn’t help that I was spending some time with the Plan +9 Operating system. More specifically +9FRONT. The way that ACME editor +handles text editing is just wonderful. Different and fresh somehow, even though +it’s super old.

So, I went on a lookout for an interesting way of visualizing results of some +query. I found these applications to be outstanding examples of how not to be a +captive of a predetermined way of doing things.

My idea is not as out there as ACME is, but it is a spin on the terminal +emulators. I like the modes that Vi/Vim provides you with. I like the way the +Emacs does its own M-x M-c. Furthermore, I really like how Mathematica and +Jupyter present the data in a free flowing form. And I love how Temple OS is +basically a C interpreter on some level.

Note: This is part 1 of the journey. Nowhere finished yet. I am just +tinkering with this at the moment. This whole thing can easily spectacularly +fail.

So I started. I knew that I wanted to have the couple of modes, but I didn’t +like the repetition of keystrokes, so the only option was to have some sort of +toggle and indicate to the user that they are in a special mode. Like Vi does +for Normal and Visual mode.

These modes would for the first version be:

  • Preview mode (toggle with Ctrl + P)
    • When this mode would be enabled, the ls command would try to find images +from the results and display thumbnails from them in the terminal itself. +No ASCII art. Proper images. In a grid!
  • Detach mode (toggle with Ctrl + D)
    • When this mode would be enabled, every command would open a new window +and execute that command in it. This would be useful for starting htop +in a separate window.

The reason for having these modes togglable is to not ask for previews every +time. You enable a mode and until you disable it, it behaves that way. Purely +out of ergonomic reasons.

I would like to treat every terminal I open as a session mentally. When I start +using the terminal, I start digging deeper into the issue I am trying to +resolve. And while I am doing this, I would like to open detached windows +etc. A lot of these things can be done easily with something like +i3, but also that pull you out of the context of what you +were doing. I would like to orchestrate everything from one single point.

In planning for this project, I knew that I would need to use a language like C +and a library such as SDL2 in order to achieve the +desired results. I had considered other options, but ultimately determined that +SDL2 was the best fit based on its capabilities and +reputation in the programming community.

At first, I thought the idea of a hardware accelerated terminal was a bit of a +joke. It seemed like such a niche and unnecessary feature, especially given the +fact that terminal emulators have been around for decades and have always relied +on software rendering. But to be fair, Alacritty is +doing the same thing. Well, they are doing a remarkable job at it.

So, I embarked on a journey. Everything has to start somewhere. For me, it +started with creating a window! It has to start somewhere. 🙂

// Oh, Hi Mark!
+// Create the window, obviously.
+SDL_Window *window = SDL_CreateWindow(
+  WINDOW_TITLE, SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
+  WINDOW_WIDTH, WINDOW_HEIGHT,
+  SDL_WINDOW_RESIZABLE | SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN);
+

I continued like this to get some text displayed on the screen.

I noted that +TTF_RenderText_Solid +rendered text really poorly. There were no antialiasing at all. In my wisdom, I +never checked the documentation. Well, that was a fail. To uneducated like me: +TTF_RenderText_Solid renders Latin1 text at fast quality to a new 8-bit +surface. So, that's why the texts looked like shit. No wonder.

Remarks on TTF_RenderText_Solid: This function will allocate a new 8-bit, +palettized surface. The surface's 0 pixel will be the colorkey, giving a +transparent background. The 1 pixel will be set to the text color.

After I replaced it with +TTF_RenderText_LCD which +renders Latin1 text at LCD subpixel quality to a new ARGB surface, the text +started looking good. Really make sure you read the documentation. It’s actually +good. As a side note, you can find all the documentation regarding SDL2 on +their Wiki.

After that was done, I started working on displaying other things like Preview +and Detach modes. This wasn’t really that hard. In SDL2 you can check all the +available events with while (SDL_PollEvent(&event) > 0) and have a bunch of +switch statements to determine which key is currently being pressed. More about +keys, SDLKey and mroe about +pooling the events on +SDL_PollEvent.

while (SDL_PollEvent(&event) > 0)
+{
+  switch (event.type)
+  {
+  case SDL_QUIT:
+    running = false;
+    break;
+
+  case SDL_TEXTINPUT:
+    if (!meta_key_pressed)
+    {
+      strncat(input_prompt_text, event.text.text, 1);
+      update_input_prompt = true;
+    }
+    break;
+	}
+}
+

After that was somewhat working correctly, I started creating a struct that +would hold all the commands and results and I call them Cells. Yes, I stole that +naming idea from Jupyter.

typedef struct
+{
+  char *command;
+  char *result;
+  SDL_Surface *surface;
+  SDL_Texture *texture;
+  SDL_Rect rect;
+} Cell;
+

I am at a place now where I am starting to implement scrolling. This will for +sure be fun to code. Memory management in C is super easy. 😂

I have also added a simple INI file like +configuration support. It is done in an +STB style of +header and maps +to specific options supported by the terminal. It is not universal, and the code +below demonstrates how I will use it in the future.

#ifndef CONFIG_H
+#define CONFIG_H
+
+/*
+# This is a comment
+
+# This is the first configuration option
+dettach=value11111
+
+# This is the second configuration option
+preview=value22222
+
+# This is the third configuration option
+debug=value33333
+*/
+
+// Define a struct to hold the configuration options
+typedef struct
+{
+    char dettach[256];
+    char preview[256];
+    char debug[256];
+} Config;
+
+// Read the configuration file and return the options as a struct
+extern Config read_config_file(const char *filename)
+{
+  // Create a struct to hold the configuration options
+  Config config = {0};
+
+  // Open the configuration file
+  FILE *file = fopen(filename, "r");
+
+  // Read each line from the file
+  char line[256];
+  while (fgets(line, sizeof(line), file))
+  {
+    // Check if this line is a comment or empty
+    if (line[0] == '#' || line[0] == '\n')
+      continue;
+
+    // Parse the line to get the option and value
+    char option[128], value[128];
+    if (sscanf(line, "%[^=]=%s", option, value) != 2)
+      continue;
+
+    // Set the value of the appropriate option in the config struct
+    if (strcmp(option, "dettach") == 0)
+    {
+      strncpy(config.option1, value, sizeof(config.option1));
+    }
+    else if (strcmp(option, "preview") == 0)
+    {
+      strncpy(config.option2, value, sizeof(config.option2));
+    }
+    else if (strcmp(option, "debug") == 0)
+    {
+      strncpy(config.option3, value, sizeof(config.option3));
+    }
+  }
+
+  // Close the configuration file
+  fclose(file);
+
+  // Return the configuration options
+  return config;
+}
+
+#endif
+

This is as far as I managed to get for now. I have a daily job and this +prohibits me to work on these things full time. But I should probably get back +and finish this. At least have a simple version working out, so I can start +testing it on my machines. Fingers crossed. 🕵️‍♂️