LOLWUT: refactoring + skeleton of LOLWUT 6.

src/lolwut.c

@@ -34,8 +34,11 @@
  */
 
 #include "server.h"
+#include "lolwut.h"
+#include <math.h>
 
 void lolwut5Command(client *c);
+void lolwut6Command(client *c);
 
 /* The default target for LOLWUT if no matching version was found.
  * This is what unstable versions of Redis will display. */
@@ -47,11 +50,127 @@ void lolwutUnstableCommand(client *c) {
     sdsfree(rendered);
 }
 
+/* LOLWUT [<version>] */
 void lolwutCommand(client *c) {
     char *v = REDIS_VERSION;
-    if ((v[0] == '5' && v[1] == '.') ||
+    char verstr[64];
+
+    if (c->argc == 2) {
+        long ver;
+        if (getLongFromObjectOrReply(c,c->argv[1],&ver,NULL) != C_OK) return;
+        snprintf(verstr,sizeof(verstr),"%u.0.0",(unsigned int)ver);
+        v = verstr;
+    }
+
+    if ((v[0] == '5' && v[1] == '.' && v[2] != '9') ||
         (v[0] == '4' && v[1] == '.' && v[2] == '9'))
         lolwut5Command(c);
+    else if ((v[0] == '6' && v[1] == '.' && v[2] != '9') ||
+             (v[0] == '5' && v[1] == '.' && v[2] == '9'))
+        lolwut6Command(c);
     else
         lolwutUnstableCommand(c);
 }
+
+/* ========================== LOLWUT Canvase ===============================
+ * Many LOWUT versions will likely print some computer art to the screen.
+ * This is the case with LOLWUT 5 and LOLWUT 6, so here there is a generic
+ * canvas implementation that can be reused.  */
+
+/* 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 lwDrawPixel(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];
+}
+
+/* Draw a line from x1,y1 to x2,y2 using the Bresenham algorithm. */
+void lwDrawLine(lwCanvas *canvas, int x1, int y1, int x2, int y2, int color) {
+    int dx = abs(x2-x1);
+    int dy = abs(y2-y1);
+    int sx = (x1 < x2) ? 1 : -1;
+    int sy = (y1 < y2) ? 1 : -1;
+    int err = dx-dy, e2;
+
+    while(1) {
+        lwDrawPixel(canvas,x1,y1,color);
+        if (x1 == x2 && y1 == y2) break;
+        e2 = err*2;
+        if (e2 > -dy) {
+            err -= dy;
+            x1 += sx;
+        }
+        if (e2 < dx) {
+            err += dx;
+            y1 += sy;
+        }
+    }
+}
+
+/* Draw a square centered at the specified x,y coordinates, with the specified
+ * rotation angle and size. In order to write a rotated square, we use the
+ * trivial fact that the parametric equation:
+ *
+ *  x = sin(k)
+ *  y = cos(k)
+ *
+ * Describes a circle for values going from 0 to 2*PI. So basically if we start
+ * at 45 degrees, that is k = PI/4, with the first point, and then we find
+ * the other three points incrementing K by PI/2 (90 degrees), we'll have the
+ * points of the square. In order to rotate the square, we just start with
+ * k = PI/4 + rotation_angle, and we are done.
+ *
+ * Of course the vanilla equations above will describe the square inside a
+ * circle of radius 1, so in order to draw larger squares we'll have to
+ * multiply the obtained coordinates, and then translate them. However this
+ * is much simpler than implementing the abstract concept of 2D shape and then
+ * performing the rotation/translation transformation, so for LOLWUT it's
+ * a good approach. */
+void lwDrawSquare(lwCanvas *canvas, int x, int y, float size, float angle, int color) {
+    int px[4], py[4];
+
+    /* Adjust the desired size according to the fact that the square inscribed
+     * into a circle of radius 1 has the side of length SQRT(2). This way
+     * size becomes a simple multiplication factor we can use with our
+     * coordinates to magnify them. */
+    size /= 1.4142135623;
+    size = round(size);
+
+    /* Compute the four points. */
+    float k = M_PI/4 + angle;
+    for (int j = 0; j < 4; j++) {
+        px[j] = round(sin(k) * size + x);
+        py[j] = round(cos(k) * size + y);
+        k += M_PI/2;
+    }
+
+    /* Draw the square. */
+    for (int j = 0; j < 4; j++)
+        lwDrawLine(canvas,px[j],py[j],px[(j+1)%4],py[(j+1)%4],color);
+}