From eb78fc66930abc70383a511c2ac8c5585f60a447 Mon Sep 17 00:00:00 2001
From: ladyada <limor@ladyada.net>
Date: Thu, 15 Mar 2012 16:23:38 -0400
Subject: [PATCH] triangles!

---
 Adafruit_GFX.cpp | 88 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 87 insertions(+), 1 deletion(-)

diff --git a/Adafruit_GFX.cpp b/Adafruit_GFX.cpp
index fef2211..40a5123 100644
--- a/Adafruit_GFX.cpp
+++ b/Adafruit_GFX.cpp
@@ -226,7 +226,7 @@ uint16_t h, uint16_t r, uint16_t color) {
 
 // fill a rounded rectangle!
 void Adafruit_GFX::fillRoundRect(uint16_t x, uint16_t y, uint16_t w,
-uint16_t h, uint16_t r, uint16_t color) {
+				 uint16_t h, uint16_t r, uint16_t color) {
   // smarter version
   fillRect(x+r, y, w-2*r, h, color);
 
@@ -235,6 +235,92 @@ uint16_t h, uint16_t r, uint16_t color) {
   fillCircleHelper(x+r    , y+r, r, 2, h-2*r-1, color);
 }
 
+// draw a triangle!
+void Adafruit_GFX::drawTriangle(uint16_t x0, uint16_t y0,
+				uint16_t x1, uint16_t y1, 
+				uint16_t x2, uint16_t y2, uint16_t color) {
+  drawLine(x0, y0, x1, y1, color);
+  drawLine(x1, y1, x2, y2, color);
+  drawLine(x2, y2, x0, y0, color);
+}
+
+// fill a triangle!
+void Adafruit_GFX::fillTriangle ( uint16_t x0, uint16_t y0,
+				     uint16_t x1, uint16_t y1, 
+				     uint16_t x2, uint16_t y2, uint16_t color) {
+
+  int16_t a, b, y, last;
+
+  // Sort coordinates by Y order (y2 >= y1 >= y0)
+  if (y0 > y1) {
+    swap(y0, y1); swap(x0, x1);
+  }
+  if (y1 > y2) {
+    swap(y2, y1); swap(x2, x1);
+  }
+  if (y0 > y1) {
+    swap(y0, y1); swap(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;
+    drawFastHLine(a, y0, b-a+1, color);
+    return;
+  }
+
+  int16_t
+    dx01 = x1 - x0,
+    dy01 = y1 - y0,
+    dx02 = x2 - x0,
+    dy02 = y2 - y0,
+    dx12 = x2 - x1,
+    dy12 = y2 - y1,
+    sa   = 0,
+    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) swap(a,b);
+    drawFastHLine(a, y, b-a+1, color);
+  }
+
+  // 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) swap(a,b);
+    drawFastHLine(a, y, b-a+1, color);
+  }
+}
 
 void Adafruit_GFX::drawBitmap(uint16_t x, uint16_t y, 
 			      const uint8_t *bitmap, uint16_t w, uint16_t h,