painter.c

#include "helpers.h"

// Given a x, y coordinate, set that pixel ON on the board
void pixon(const BYTE x, const BYTE y)
{
    if (x < SCREEN_X_MIN || x > SCREEN_X_MAX || y < SCREEN_Y_MIN || y > SCREEN_Y_MAX)
        return;

    // Determine which row the bit is (there are 8 bits in each row so we divide by 8)
    BYTE row = y >> 3;

    // Multiply row by 128 (<< 7) to push it in the correct place Y position in the buffer (now at (0,Y)). Add X to push it to the correct column (X,Y)
    int buf_coord = (row << 7) + x;

    // We want to know which bit of that int we want to modify, so we get the last three bits (0-7) which tell us the bit offset aka modulo 8
    row = y & 7;

    // We push a one with that many steps forward in that int in the buffer and or it to make it 1 at the specific bit
    display_buffer[buf_coord] |= 1 << row;
}

// Given a x, y coordinate, set that pixel OFF on the board
void pixoff(const BYTE x, const BYTE y)
{
    if (x < SCREEN_X_MIN || x > SCREEN_X_MAX || y < SCREEN_Y_MIN || y > SCREEN_Y_MAX)
        return;

    // Determine which row the bit is (there are 8 bits in each row so we divide by 8)
    BYTE row = y >> 3;

    // Multiply row by 128 (<< 7) to push it in the correct place Y position in the buffer (now at (0,Y)). Add X to push it to the correct column (X,Y)
    int buf_coord = (row << 7) + x;

    // We want to know which bit of that int we want to modify, so we get the last three bits (0-7) which tell us the bit offset aka modulo 8
    row = y & 7;

    // We push a one with that many steps forward in that int in the buffer and and it with the inverse of that int to make it 0 at the specific bit
    display_buffer[buf_coord] &= ~(1 << row);
}

/**
 * Draws a line between the points (x0, y0) and (x1, y1) using Bresenham's line algorithm.
 */
void draw_line(int x0, int y0, const int x1, const int y1)
{
    int dx = x1 - x0,
        dy = y1 - y0,
        sx = x0 < x1 ? 1 : -1,
        sy = y0 < y1 ? 1 : -1;
    dx = dx > 0 ? dx : -dx;
    dy = dy > 0 ? -dy : dy;
    int error = dx + dy,
        e2;

    while (1)
    {
        pixon(x0, y0);
        if (x0 == x1 && y0 == y1)
            break;

        e2 = 2 * error;
        if (e2 >= dy)
        {
            if (x0 == x1)
                break;
            error = error + dy;
            x0 = x0 + sx;
        }
        if (e2 <= dx)
        {
            if (y0 == y1)
                break;
            error = error + dx;
            y0 = y0 + sy;
        }
    }
}

// Clears the buffer by making all its values to 0
void clear_buf()
{
    int i;
    for (i = 0; i < OLED_BUF_SIZE; i++)
        display_buffer[i] = 0;
}