Fixed gaps in line and simplified code

In some cases when adding extra pixel between steep and non-steep 
aaline, one extra pixel is not enough, causing gaps to appear between 
aalines
Instead both endpoint pixels are needed
This allowed to merge extra pixel handling with endpoint handling

Author: mzivic7

src_c/draw.c

@@ -1329,7 +1329,6 @@ draw_aaline(SDL_Surface *surf, Uint32 color, float from_x, float from_y,
     Uint32 pixel_color;
     float x_gap, y_endpoint, clip_left, clip_right, clip_top, clip_bottom;
     int steep, y;
-    int line_inverted;
 
     dx = to_x - from_x;
     dy = to_y - from_y;
@@ -1362,7 +1361,6 @@ draw_aaline(SDL_Surface *surf, Uint32 color, float from_x, float from_y,
         swap(&clip_right, &clip_bottom);
     }
     if (dx < 0) {
-        line_inverted = 1;
         swap(&from_x, &to_x);
         swap(&from_y, &to_y);
         dx = -dx;
@@ -1427,9 +1425,11 @@ draw_aaline(SDL_Surface *surf, Uint32 color, float from_x, float from_y,
 
     /* Handle endpoints separately.
      * The line is not a mathematical line of thickness zero. The same
-     * goes for the endpoints. The have a height and width of one pixel. */
+     * goes for the endpoints. The have a height and width of one pixel.
+     * Extra pixel drawing is requested externally from aalines.
+     * It is drawn only when one line is steep and other is not.*/
     /* First endpoint */
-    if (!disable_first_endpoint) {
+    if (!disable_first_endpoint || extra_pixel_for_aalines) {
         x_pixel_start = (int)from_x;
         y_endpoint = intersect_y =
             from_y + gradient * (x_pixel_start - from_x);
@@ -1463,38 +1463,14 @@ draw_aaline(SDL_Surface *surf, Uint32 color, float from_x, float from_y,
             x_pixel_start++;
         }
     }
-    else {
-        /* Handle extra pixel for aalines.
-         * It is drawn only when one line is steep and other is not.*/
-        if (extra_pixel_for_aalines && !line_inverted) {
-            x_pixel_start = (int)from_x;
-            y_endpoint = intersect_y =
-                from_y + gradient * (x_pixel_start - from_x);
-            if (to_x > clip_left + 1.0f) {
-                x_gap = 1 + x_pixel_start - from_x;
-                brightness = y_endpoint - (int)y_endpoint;
-                if (steep) {
-                    x = (int)y_endpoint;
-                    y = x_pixel_start;
-                }
-                else {
-                    x = x_pixel_start;
-                    y = (int)y_endpoint;
-                }
-                if ((int)y_endpoint < y_endpoint) {
-                    pixel_color = get_antialiased_color(surf, x, y, color,
-                                                        brightness * x_gap);
-                    set_and_check_rect(surf, x, y, pixel_color, drawn_area);
-                }
-            }
-        }
-        /* To be sure main loop skips first endpoint.*/
+    /* To be sure main loop skips first endpoint.*/
+    if (disable_first_endpoint) {
         x_pixel_start = (int)ceil(from_x);
         intersect_y = from_y + gradient * (x_pixel_start - from_x);
     }
     /* Second endpoint */
     x_pixel_end = (int)ceil(to_x);
-    if (!disable_second_endpoint) {
+    if (!disable_second_endpoint || extra_pixel_for_aalines) {
         if (from_x < clip_right - 1.0f) {
             y_endpoint = to_y + gradient * (x_pixel_end - to_x);
             x_gap = 1 - x_pixel_end + to_x;
@@ -1524,29 +1500,6 @@ draw_aaline(SDL_Surface *surf, Uint32 color, float from_x, float from_y,
             set_and_check_rect(surf, x, y, pixel_color, drawn_area);
         }
     }
-    else {
-        /* Handle extra pixel for aalines.
-         * It is drawn only when one line is steep and other is not.*/
-        if (extra_pixel_for_aalines && line_inverted) {
-            if (from_x < clip_right - 1.0f) {
-                y_endpoint = to_y + gradient * (x_pixel_end - to_x);
-                x_gap = 1 - x_pixel_end + to_x;
-                brightness = y_endpoint - (int)y_endpoint;
-                if (steep) {
-                    x = (int)y_endpoint - 1;
-                    y = x_pixel_end;
-                }
-                else {
-                    x = x_pixel_end;
-                    y = (int)y_endpoint - 1;
-                }
-                brightness = 1 - brightness;
-                pixel_color = get_antialiased_color(surf, x, y, color,
-                                                    brightness * x_gap);
-                set_and_check_rect(surf, x, y, pixel_color, drawn_area);
-            }
-        }
-    }
 
     /* main line drawing loop */
     for (x = x_pixel_start; x < x_pixel_end; x++) {