Adds cross stitch function to library and new documentation folder

demo/Makefile

@@ -1,10 +1,16 @@
-all: demo
+all: demo cross-stitch-demo
 
 demo: demo.o
 	clang++ demo.o ../src/libturtle.a ../src/libpoint.a ../libembroidery/libembroidery.a -o demo
 
 demo.o: demo.cpp
 	clang++ -g -c -std=c++1z -Wall -Wextra -pedantic -I../libembroidery demo.cpp
 
+cross-stitch-demo: cross-stitch-demo.o
+	clang++ cross-stitch-demo.o ../src/libturtle.a ../src/libpoint.a ../libembroidery/libembroidery.a -o cross-stitch-demo
+
+cross-stitch-demo.o: cross-stitch-demo.cpp
+	clang++ -g -c -std=c++1z -Wall -Wextra -pedantic -I../libembroidery cross-stitch-demo.cpp
+
 clean:
 	rm *.o demo

doc/cross-stitch-demo.md

@@ -0,0 +1,10 @@
+# Cross stitching demo
+This demo takes you through how to use the Turtle's cross stitching function. Cross stitching is the process of making an image out of many small x shaped stitches. Example: https://www.needlework-tips-and-techniques.com/images/homemade-valentines-cards.jpg
+## Step 1. Find a pattern you like
+Go on line and find a cross stitch pattern you like, or create your own on graph paper! You should have a couple colors in mind, and know at what coordinate you would like each of those colors to be filled in. 
+## Step 2. Convert this to a vector of coordinates
+Make a different vector of coordinates for each color that you have, placing them in the same C file. It should be a vector of pairs, as shown in the cross-stitch-demo.cpp file in the demo folder.
+## Step 3. Add alignment-helper coordinates
+Add the pair {0,0} to each of your vectors. The reason we do this is so, when we embroider each layer, we can align them against your embroidery piece at the {0,0} point. Otherwise, it is impossible to tell at what part on the fabric we should be embroidering the next layer. (You can also use an arbitrarily large point, like {20,20}).
+## Step 4. Embroidery!
+Pass your vector into the Turtle's provided function as shown in cross-stitch-demo.cpp. Compile and run, and your file should be generated! Do this as many times as you need, and upload your DST files onto the machine and embroider them separately. 

src/turtle.cpp

@@ -360,6 +360,44 @@ void Turtle::check_density(const Point& pos) {
     density_error_ |= (entry->second > DENSITY_ERROR_LIMIT);
 }
 
+// draws an X of fixed size at (x,y)
+void Turtle::drawX(int x, int y) {
+    right(45);
+    gotopoint(x,y);
+
+    pendown();
+    forward(10);
+    penup();
+    left(45);
+    left(45);
+
+    gotopoint(x+9,y);
+    pendown();
+    backward(10);
+    penup();
+    right(45);
+}
+
+// given a list of coordinates on a 1x1 grid, stitch the cross stitches of fixed size
+void Turtle::createCrossStitchPattern(std::vector<std::pair<int, int>>& coordinates) {
+
+    for (std::pair<int, int>& coord : coordinates) {
+        coord.first *= 6;
+        coord.second *= 6;
+    }  
+
+    // draw a random stitch as a reference point
+    gotopoint(0,0);
+    pendown();
+    forward(5);
+    penup();
+
+    for (const auto& coord : coordinates) {
+        drawX(coord.first, coord.second);  // Draw the X at each coordinate
+    }
+
+}
+
 /* Disabled functions -- we could use these at some point, but they feel too
 high-level for providing to CS70
 

src/turtle.hpp

@@ -35,6 +35,8 @@ class Turtle {
 
     void displayMessage(std::string message, float scale);
 
+   void createCrossStitchPattern(std::vector<std::pair<int, int>>& coordinates);
+
     void save(std::string fname);
     void end();
 
@@ -51,6 +53,7 @@ class Turtle {
     void set_y(const float y);
     void increment_x(const float x);
     void increment_y(const float y);
+    void drawX(int x, int y);
     // void rectangle(float w, float h);
     // void circle(float radius);
     // void snowflake(float sidelength, int levels);