line drawing

.gitignore

@@ -1,2 +1,3 @@
 main
 *.o
+*.ppm

README.md

@@ -1,3 +1,3 @@
 # libpaint
 
-Software rasterizer
+Software rasterizer

main.c

@@ -5,6 +5,7 @@ int main() {
     lp_painter *painter = lp_painter_create(512, 512);
     lp_painter_fill_rect(painter, lp_rgb(255, 0, 0), 0, 0, 512, 512);
     lp_painter_fill_rect(painter, lp_rgb(0, 0, 255), 0, 25, 103, 40);
+    lp_painter_line(painter, lp_rgb(0, 255, 0), 0, 511, 511, 0);
     lp_painter_save_ppm(painter, "./surface.ppm");
     lp_painter_free(painter);
 }

painter.c

@@ -11,6 +11,7 @@ lp_painter *lp_painter_create(size_t width, size_t height) {
     lp_pixel *buf = malloc(width * height * sizeof(lp_pixel));
 
     painter->buf = buf;
+    painter->buf_length = width * height;
     painter->width = width;
     painter->height = height;
 
@@ -26,11 +27,75 @@ void lp_painter_free(lp_painter *painter) {
     }
 }
 
+static inline void lp_painter_put_pixel(lp_painter *painter, lp_pixel color, size_t x, size_t y) {
+    size_t index = y * painter->width + x;
+    painter->buf[index] = color;
+}
+
 void lp_painter_fill_rect(lp_painter *painter, lp_pixel fill_color, size_t pos_x, size_t pos_y, size_t width, size_t height) {
     for (size_t y = pos_y; y < pos_y + height; y++) {
         for (size_t x = pos_x; x < pos_x + width; x++) {
-            size_t index = y * painter->width + x;
+            lp_painter_put_pixel(painter, fill_color, pos_x, pos_y);
-            painter->buf[index] = fill_color;
+        }
+    }
+}
+
+void _lp_painter_line_low(lp_painter *p, lp_pixel color, int32_t x0, int32_t y0, int32_t x1, int32_t y1) {
+    int32_t dx = x1 - x0;
+    int32_t dy = y1 - y0;
+    int32_t y_inc = 1;
+    if (dy < 0) {
+        y_inc = -1;
+        dy = -dy;
+    }
+    int32_t d = dy * 2 - dx;
+    int32_t y = y0;
+    
+    for (int32_t x = x0; x < x1; x++) {
+        lp_painter_put_pixel(p, color, x, y);
+        if (d > 0) {
+            y += y_inc;
+            d += 2 * (dy - dx);
+        } else {
+            d += 2 * dy;
+        }
+    }
+}
+
+
+void _lp_painter_line_high(lp_painter *p, lp_pixel color, int32_t x0, int32_t y0, int32_t x1, int32_t y1) {
+    int32_t dx = x1 - x0;
+    int32_t dy = y1 - y0;
+    int32_t x_inc = 1;
+    if (dx < 0) {
+        x_inc = -1;
+        dx = -dx;
+    }
+    int32_t d = dx * 2 - dy;
+    int32_t x = x0;
+    
+    for (int32_t y = y0; y < y1; y++) {
+        lp_painter_put_pixel(p, color, x, y);
+        if (d > 0) {
+            x += x_inc;
+            d += 2 * (dx - dy);
+        } else {
+            d += 2 * dx;
+        }
+    }
+}
+void lp_painter_line(lp_painter *p, lp_pixel color, int32_t x0, int32_t y0, int32_t x1, int32_t y1) {
+    if (abs(y1 - y0) < abs(x1 -x0)) {
+        if (x0 > x1) {
+            _lp_painter_line_low(p, color, x1, y1, x0, y0);
+        } else {
+            _lp_painter_line_low(p, color, x0, y0, x1, y1);
+        }
+    } else {
+        if (y0 > y1) {
+            _lp_painter_line_high(p, color, x1, y1, x0, y0);
+        } else {
+            _lp_painter_line_high(p, color, x0, y0, x1, y1);
         }
     }
 }

painter.h

@@ -16,12 +16,13 @@ typedef struct lp_painter {
     lp_pixel *buf;
     size_t width;
     size_t height;
+    size_t buf_length;
 } lp_painter;
 
 lp_painter *lp_painter_create();
 void lp_painter_free(lp_painter *painter);
 void lp_painter_fill_rect(lp_painter *painter, lp_pixel fill_color, size_t pos_x, size_t pos_y, size_t width, size_t height);
 void lp_painter_save_ppm(lp_painter *painter, const char *filename);
-
+void lp_painter_line(lp_painter *p, lp_pixel color, int32_t x0, int32_t y0, int32_t x1, int32_t y1);
 
 #endif