Extend gpanel library with fill rectangle routine.

src/libgpanel/Makefile

@@ -5,8 +5,8 @@ CFLAGS          += -O -Wall -Werror
 MAN             = gpanel.0
 MANSRC          = gpanel.3
 
-OBJS    	= open.o clear.o pixel.o line.o rect.o fill.o circle.o \
-                  image.o char.o text.o text_width.o
+OBJS    	= open.o clear.o pixel.o line.o rect.o fill.o fill_triangle.o \
+                  circle.o image.o char.o text.o text_width.o
 
 all:    	../libgpanel.a $(MAN)
 

src/libgpanel/fill_triangle.c

@@ -0,0 +1,125 @@
+/*
+ * Fill a triangle.
+ * Code ported from AdaFruit TFT LCD library.
+ *
+ * Copyright (C) 2015 Serge Vakulenko, <serge@vak.ru>
+ *
+ * Permission to use, copy, modify, and distribute this software
+ * and its documentation for any purpose and without fee is hereby
+ * granted, provided that the above copyright notice appear in all
+ * copies and that both that the copyright notice and this
+ * permission notice and warranty disclaimer appear in supporting
+ * documentation, and that the name of the author not be used in
+ * advertising or publicity pertaining to distribution of the
+ * software without specific, written prior permission.
+ *
+ * The author disclaim all warranties with regard to this
+ * software, including all implied warranties of merchantability
+ * and fitness.  In no event shall the author be liable for any
+ * special, indirect or consequential damages or any damages
+ * whatsoever resulting from loss of use, data or profits, whether
+ * in an action of contract, negligence or other tortious action,
+ * arising out of or in connection with the use or performance of
+ * this software.
+ */
+#include <sys/ioctl.h>
+#include <sys/gpanel.h>
+
+/*
+ * Swap values of two integer variables.
+ */
+#define swapi(x,y) { int _t = x; x = y; y = _t; }
+
+void gpanel_fill_triangle(int color, int x0, int y0,
+    int x1, int y1, int x2, int y2)
+{
+    int a, b, y, last;
+
+    // Sort coordinates by Y order (y2 >= y1 >= y0)
+    if (y0 > y1) {
+        swapi(y0, y1);
+        swapi(x0, x1);
+    }
+    if (y1 > y2) {
+        swapi(y2, y1);
+        swapi(x2, x1);
+    }
+    if (y0 > y1) {
+        swapi(y0, y1);
+        swapi(x0, x1);
+    }
+
+    if (y0 == y2) {
+        // Handle awkward all-on-same-line case as its own thing
+        a = b = x0;
+
+        if (x1 < a)
+            a = x1;
+        else if (x1 > b)
+            b = x1;
+
+        if (x2 < a)
+            a = x2;
+        else if (x2 > b)
+            b = x2;
+
+        gpanel_fill(color, a, y0, b-a+1, y0);
+        return;
+    }
+
+    int dx01 = x1 - x0;
+    int dy01 = y1 - y0;
+    int dx02 = x2 - x0;
+    int dy02 = y2 - y0;
+    int dx12 = x2 - x1;
+    int dy12 = y2 - y1;
+    int sa = 0;
+    int sb = 0;
+
+    // For upper part of triangle, find scanline crossings for segments
+    // 0-1 and 0-2.  If y1=y2 (flat-bottomed triangle), the scanline y1
+    // is included here (and second loop will be skipped, avoiding a /0
+    // error there), otherwise scanline y1 is skipped here and handled
+    // in the second loop...which also avoids a /0 error here if y0=y1
+    // (flat-topped triangle).
+    if (y1 == y2)
+        last = y1;      // Include y1 scanline
+    else
+        last = y1-1;    // Skip it
+
+    for (y=y0; y<=last; y++) {
+        a   = x0 + sa / dy01;
+        b   = x0 + sb / dy02;
+        sa += dx01;
+        sb += dx02;
+
+        /* longhand:
+         * a = x0 + (x1 - x0) * (y - y0) / (y1 - y0);
+         * b = x0 + (x2 - x0) * (y - y0) / (y2 - y0);
+         */
+        if (a > b)
+            swapi(a, b);
+
+        gpanel_fill(color, a, y, b-a+1, y);
+    }
+
+    // For lower part of triangle, find scanline crossings for segments
+    // 0-2 and 1-2.  This loop is skipped if y1=y2.
+    sa = dx12 * (y - y1);
+    sb = dx02 * (y - y0);
+    for (; y<=y2; y++) {
+        a   = x1 + sa / dy12;
+        b   = x0 + sb / dy02;
+        sa += dx12;
+        sb += dx02;
+
+        /* longhand:
+         * a = x1 + (x2 - x1) * (y - y1) / (y2 - y1);
+         * b = x0 + (x2 - x0) * (y - y0) / (y2 - y0);
+         */
+        if (a > b)
+            swapi(a, b);
+
+        gpanel_fill(color, a, y, b-a+1, y);
+    }
+}

sys/include/gpanel.h

@@ -112,6 +112,7 @@ void gpanel_pixel(int color, int x, int y);
 void gpanel_line(int color, int x0, int y0, int x1, int y1);
 void gpanel_rect(int color, int x0, int y0, int x1, int y1);
 void gpanel_fill(int color, int x0, int y0, int x1, int y1);
+void gpanel_fill_triangle(int color, int x0, int y0, int x1, int y1, int x2, int y2);
 void gpanel_circle(int color, int x, int y, int radius);
 void gpanel_image(int x, int y, int width, int height, const unsigned short *data);
 void gpanel_char(const struct gpanel_font_t *font, int color, int background, int x, int y, int sym);