How to display graphical text without X using C?

Question

Using the Raspberry Pi 2 with the official 7" touchscreen, I want to display some high quality text without using an Xorg server. I'm looking for APIs that provide simple functions such as:

Render_text ("hello", x,y, blue, size, "nicefontX");

Such a library could be build on top of the linux kernel framebuffer or openGLES/VG. I have found at least one such thing that appears to be pi specific.

Again, I am interested in C -- I have already found many things involving python.

• goldilocks: Zogger -> I think I may have been wrong about not referring to this as the framebuffer, since everything that does this seems to require it be built into the kernel -- all apologies. But I'm still sure I'm right about the fact that you will find much more material here if you search beyond "raspberry pi". Anyway, good luck.
• goldilocks: BTW, I can't provide a complete answer, but it looks to me like SDL runs on the Pi using the framebuffer -- although again examples of its use won't be pi specific (if you keep waiting for that, you are going to be waiting a long time, honestly). Anyway, I am pretty sure it does have text features, although it has been 6-7 years since I used it.

Answer 1

Did you consider 2D Game engines/libraries ? Because OpenGL/OpenVG are very low-level and don't do font handling , the added "belt and suspenders" of those libs will make your life much easier :

http://www.raylib.com/

https://github.com/raysan5/raylib

Answer 2

I got 2D vector graphics library working, using it from C Language, currently with a 128x128 OLED display on a headless Raspberry Pi 3B, using the following recipe. Note: X-Windows (X11) is not installed (e.g. Raspian lite edition). As for performance considerations, OpenVG's claim to fame is that it utilizes available HW acceleration layer(s) rather than just load the CPU.

1. Install: Raspian lite edition

2. Install: fbcp-ili9341: "Blazingly fast display driver for SPI-based LCD displays for Raspberry Pi A,B,2,3, and Zero"

   I built that from source, and configured the the GPIO pins SPI pins via the (documented) -D commands on the compiler line. For example:

   # cmake -DSSD1351=ON -DGPIO_TFT_DATA_CONTROL=25 -DGPIO_TFT_RESET_PIN=24 -DSPI_BUS_CLOCK_DIVISOR=30 -DARMV8A=ON \ ..
   

   and then proved it work sanity tested it by writing stuff to /dev/fb0.

3. Didn't need to install OpenGL libraries on my Raspian systems, because they seemed to be pre-installed at /opt/vc/lib, opt/vc/include.

   However, I created the following symlinks:

   # cd /opt/vc/lib
   # ln -s libbrcmGLESv2.so libGLESv2.so
   # ln -s libbrcmEGL.so libEGL.so
   

4. OpenVG "The Standard for Vector Graphics Acceleration"

   https://github.com/ajstarks/openvg
   

5. Compiled the following C program and ran it. Worked perfectly.

   $ cc -o demo demo.c -I/opt/vc/include -Lopt/vc/lib -lshapes
   #include <stdio.h>
   #include <stdlib.h>
   #include <stddef.h>
   #include <stdint.h>
   #include <unistd.h>
   #include "VG/openvg.h"
   #include "VG/vgu.h"
   #include "fontinfo.h"
   #include "shapes.h"
   int main() {
    int width, height;
    char s[3];
    init(&width, &height); // Graphics initialization
    Start(width, height); // Start the picture
    Background(0, 50, 0); // Black background
    Fill(44, 77, 232, 1); // Big blue marble
    Circle(width / 2, 0, width); // The "world"
    Fill(255, 255, 255, 1); // White text
    TextMid(width / 2, height / 2, 
    "hello, world", 
    SerifTypeface, width / 10); // Greetings 
    End(); // End the picture
    fgets(s, 2, stdin); // look at the pic, end with [RETURN]
    finish(); // Graphics cleanup
    exit(0);
   }
   

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