LOLWUT: Rendering of the virtual canvas to a string.

src/lolwut.c

@@ -33,16 +33,18 @@
  * each new version of Redis.
  */
 
+#include "server.h"
+
 /* This function represents our canvas. Drawing functions will take a pointer
  * to a canvas to write to it. Later the canvas can be rendered to a string
  * suitable to be printed on the screen, using unicode Braille characters. */
-struct lwCanvas {
+typedef struct lwCanvas {
     int width;
     int height;
     char *pixels;
-};
+} lwCanvas;
 
-/* Translate a group of 8 pixels (2x8 vertical rectangle) to the corresponding
+/* Translate a group of 8 pixels (2x4 vertical rectangle) to the corresponding
  * braille character. The byte should correspond to the pixels arranged as
  * follows, where 0 is the least significant bit, and 7 the most significant
  * bit:
@@ -56,14 +58,83 @@ struct lwCanvas {
  * pointed by 'output'.
  */
 #include <stdio.h>
-void lwEmitPixelsGroup(int byte, char *output) {
+void lwTranslatePixelsGroup(int byte, char *output) {
     int code = 0x2800 + byte;
     /* Convert to unicode. This is in the U0800-UFFFF range, so we need to
      * emit it like this in three bytes:
      * 1110xxxx 10xxxxxx 10xxxxxx. */
-    output[1] = 0xE0 | (code >> 12);          /* 1110-xxxx */
+    output[0] = 0xE0 | (code >> 12);          /* 1110-xxxx */
-    output[2] = 0x80 | ((code >> 6) & 0x3F);  /* 10-xxxxxx */
+    output[1] = 0x80 | ((code >> 6) & 0x3F);  /* 10-xxxxxx */
-    output[3] = 0x80 | (code & 0x3F);         /* 10-xxxxxx */
+    output[2] = 0x80 | (code & 0x3F);         /* 10-xxxxxx */
 }
 
+/* Allocate and return a new canvas of the specified size. */
+lwCanvas *lwCreateCanvas(int width, int height) {
+    lwCanvas *canvas = zmalloc(sizeof(*canvas));
+    canvas->width = width;
+    canvas->height = height;
+    canvas->pixels = zmalloc(width*height);
+    memset(canvas->pixels,0,width*height);
+    return canvas;
+}
 
+/* Free the canvas created by lwCreateCanvas(). */
+void lwFreeCanvas(lwCanvas *canvas) {
+    zfree(canvas->pixels);
+    zfree(canvas);
+}
+
+/* Set a pixel to the specified color. Color is 0 or 1, where zero means no
+ * dot will be displyed, and 1 means dot will be displayed.
+ * Coordinates are arranged so that left-top corner is 0,0. You can write
+ * out of the size of the canvas without issues. */
+void lwPutPixel(lwCanvas *canvas, int x, int y, int color) {
+    if (x < 0 || x >= canvas->width ||
+        y < 0 || y >= canvas->height) return;
+    canvas->pixels[x+y*canvas->width] = color;
+}
+
+/* Return the value of the specified pixel on the canvas. */
+int lwGetPixel(lwCanvas *canvas, int x, int y) {
+    if (x < 0 || x >= canvas->width ||
+        y < 0 || y >= canvas->height) return 0;
+    return canvas->pixels[x+y*canvas->width];
+}
+
+/* Converts the canvas to an SDS string representing the UTF8 characters to
+ * print to the terminal in order to obtain a graphical representaiton of the
+ * logical canvas. The actual returned string will require a terminal that is
+ * width/2 large and height/4 tall in order to hold the whole image without
+ * overflowing or scrolling, since each Barille character is 2x4. */
+sds lwRenderCanvas(lwCanvas *canvas) {
+    sds text = sdsempty();
+    for (int y = 0; y < canvas->height; y += 4) {
+        for (int x = 0; x < canvas->width; x += 2) {
+            /* We need to emit groups of 8 bits according to a specific
+             * arrangement. See lwTranslatePixelsGroup() for more info. */
+            int byte = 0;
+            if (lwGetPixel(canvas,x,y)) byte |= (1<<0);
+            if (lwGetPixel(canvas,x,y+1)) byte |= (1<<1);
+            if (lwGetPixel(canvas,x,y+2)) byte |= (1<<2);
+            if (lwGetPixel(canvas,x+1,y)) byte |= (1<<3);
+            if (lwGetPixel(canvas,x+1,y+1)) byte |= (1<<4);
+            if (lwGetPixel(canvas,x+1,y+2)) byte |= (1<<5);
+            if (lwGetPixel(canvas,x,y+3)) byte |= (1<<6);
+            if (lwGetPixel(canvas,x+1,y+3)) byte |= (1<<7);
+            char unicode[3];
+            lwTranslatePixelsGroup(byte,unicode);
+            text = sdscatlen(text,unicode,3);
+        }
+        if (y != canvas->height-1) text = sdscatlen(text,"\n",1);
+    }
+    return text;
+}
+
+int main(void) {
+    lwCanvas *c = lwCreateCanvas(80,80);
+    for (int i = 0; i < 40; i++) {
+        lwPutPixel(c,i,i,1);
+    }
+    sds rendered = lwRenderCanvas(c);
+    printf("%s\n", rendered);
+}