draw gridlines

main.c

@@ -16,6 +16,7 @@
 #include "Crystalfontz128x128_ST7735.h"
 #include <stdio.h>
 #include "buttons.h"
+#include "grlib/grlib.h"
 #include "sampling.h"
 #include <math.h>
 #include "inc/hw_memmap.h"
@@ -79,6 +80,25 @@ int main(void) {
     while (true) {
         GrContextForegroundSet(&sContext, ClrBlack);
         GrRectFill(&sContext, &rectFullScreen); // fill screen with black
+        
+        // assumming square lcd
+        #define HEIGHT LCD_VERTICAL_MAX
+        #define PIXELS_PER_DIV 20
+
+        GrContextForegroundSet(&sContext, ClrBlue);
+
+        uint8_t xy_pos;
+        // draw gridlines from the center out
+        for (xy_pos = HEIGHT/2; xy_pos < HEIGHT; xy_pos += PIXELS_PER_DIV) {
+            GrLineDrawV(&sContext, xy_pos, 0, 128); // right
+            GrLineDrawV(&sContext, HEIGHT - xy_pos, 0, 128); // left
+
+            GrLineDrawH(&sContext, 0, 128, xy_pos); // down
+            GrLineDrawH(&sContext, 0, 128, HEIGHT - xy_pos); // up
+        }
+
+
+
         time = gTime; // read shared global only once
 
         uint32_t hundredths = time % 100;