Drawing Fonts on screen in C - c

Question

I emulated a screen with the SDL library. I want to draw fonts on this screen, simply using a "draw_pixel" function I already made.
I searched a lot on the Internet.
I found this website http://jared.geek.nz/2014/jan/custom-fonts-for-microcontrollers and the code works well. However it does not support variable-width characters
I only want to use source code.
Could you please tell me if there is a source code or a light library to draw fonts from pixels ?
EDIT : Here is my code I changed from M Oehm answer.
int DrawChar(char c, uint8_t x, uint8_t y, int r, int g, int b, SDL_Surface *rectangle, SDL_Surface *ecran, SDL_Rect position)
{
uint8_t i,j;
// Convert the character to an index
c = c & 0x7F;
if (c < ' ') {
c = 0;
} else {
c -= ' ';
}
const uint8_t* chr = font[c];
int w = chr[0];
chr++;
for (j = 0; j < w; j++) {
for (i = 0; i < CHAR_HEIGHT; i++) {
if (chr[j] & (1 << i)) {
draw_pixel(x+j, y+i, r, g, b, rectangle, ecran, position);
}
}
}
return w + CHAR_GAP;
}
void DrawString(const char* str, uint8_t x, uint8_t y, int r, int g, int b, SDL_Surface *rectangle, SDL_Surface *ecran, SDL_Rect position)
{
while (*str) {
x += DrawChar(*str++, x, y, r, g, b, rectangle, ecran, position);
}
}
const unsigned char font[96][6] = {
{3, 0x00, 0x00, 0x00}, //
{3, 0x00, 0x2f, 0x00}, // !
{4, 0x03, 0x00, 0x00, 0x03}, // "
Here is the result : The characters are still at the same size.
http://hpics.li/d54f000
EDIT :
The solution is here http://www.riuson.com/lcd-image-converter
You will have to change a bit the code because they are some mistakes, but it works.

Answer 1

You can easily extend the given code to variable-width characters. Change the definition of the font:
const unsigned char font[96][10] = {
{3, 0x00, 0x00, 0x00}, //
{3, 0x00, 0x2f, 0x00}, // !
{4, 0x03, 0x00, 0x00, 0x03}, // "
...
};
The first entry is the width of the character. The second dimension must be chosen to accomodate the widest character. It can be 9 pixels wide in this example.
Then extend the DrawChar function to use the given width and alo to return the width that the drwing position should advance, which is the width of the character plus a certain gap. (You can make the gap a parameter, so that you can print double-spaced text.)
The DrawString function then makes use of the returned width:
int DrawChar(char c, uint8 x, uint8 y, uint8 brightness)
{
uint8 i, j;
// Convert the character to an index
c = c & 0x7F;
if (c < ' ') {
c = 0;
} else {
c -= ' ';
}
const uint8* chr = font[c];
int w = chr[0];
chr++;
for (j = 0; j < w; j++) {
for (i = 0; i < CHAR_HEIGHT; i++) {
if (chr[j] & (1 << i)) {
DrawPixel(x + j, y + i, brightness);
}
}
}
return w + CHAR_GAP;
}
void DrawString(const char* str, uint8 x, uint8 y, uint8 brightness)
{
while (*str) {
x += DrawChar(*str++, x, y, brightness);
}
}
Edit: Here's a more complete example which defines only some letters:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
typedef unsigned char uint8;
char screen[25][80];
#define CHAR_HEIGHT 8
#define CHAR_GAP 2
const unsigned char font[96][10] = {
[' ' - 32] = {1, 0x00},
['A' - 32] = {5, 0x3e, 0x09, 0x09, 0x09, 0x3e},
['B' - 32] = {5, 0x3f, 0x25, 0x25, 0x25, 0x19},
['D' - 32] = {5, 0x3f, 0x21, 0x21, 0x21, 0x1e},
['E' - 32] = {5, 0x3f, 0x25, 0x25, 0x25, 0x21},
['H' - 32] = {5, 0x3f, 0x04, 0x04, 0x04, 0x3f},
['I' - 32] = {1, 0x3f},
['L' - 32] = {4, 0x3f, 0x20, 0x20, 0x20},
['M' - 32] = {7, 0x3f, 0x02, 0x04, 0x18, 0x04, 0x02, 0x3f},
['O' - 32] = {5, 0x1e, 0x21, 0x21, 0x21, 0x1e},
['P' - 32] = {5, 0x3f, 0x09, 0x09, 0x09, 0x06},
['R' - 32] = {5, 0x3f, 0x09, 0x19, 0x19, 0x26},
['S' - 32] = {5, 0x22, 0x25, 0x25, 0x25, 0x19},
['W' - 32] = {7, 0x07, 0x38, 0x0c, 0x03, 0x0c, 0x38, 0x07},
};
void DrawPixel(int x, int y, uint8 c)
{
screen[y][x] = c;
}
int DrawChar(char c, uint8 x, uint8 y, uint8 brightness)
{
uint8 i, j;
// Convert the character to an index
c = c & 0x7F;
if (c < ' ') {
c = 0;
} else {
c -= ' ';
}
const uint8* chr = font[c];
int w = chr[0];
chr++;
for (j = 0; j < w; j++) {
for (i = 0; i < CHAR_HEIGHT; i++) {
if (chr[j] & (1 << i)) {
DrawPixel(x + j, y + i, brightness);
}
}
}
return w + CHAR_GAP;
}
void DrawString(const char* str, uint8 x, uint8 y, uint8 brightness)
{
while (*str) {
x += DrawChar(*str++, x, y, brightness);
}
}
int main()
{
int i;
memset(screen, '.', sizeof(screen));
DrawString("HELLO WORLD", 2, 2, 'O');
DrawString("MISSISSIPPI", 8, 10, '#');
for (i = 0; i < 25; i++) printf("%.80s\n", screen[i]);
return 0;
}