1 files changed, 86 insertions, 0 deletions
diff --git a/lib/hitomezashi.c b/lib/hitomezashi.c
new file mode 100644
index 0000000..09feb11
--- /dev/null
+++ b/lib/hitomezashi.c
@@ -0,0 +1,86 @@
+#include "hitomezashi.h"
+#include "SDL.h"
+#include <assert.h>
+
+SDL_Color HITOMEZASHI_FG_COLOUR = {.r = 0, .g = 0, .b = 0};
+SDL_Color HITOMEZASHI_BG_COLOUR = {.r = 255, .g = 255, .b = 255};
+
+enum Hitomezashi_State_Init_Result
+hitomezashi_state_init(struct Hitomezashi_State *state, int x_pattern_len,
+                       int y_pattern_len, char *x_pattern, char *y_pattern,
+                       int gap, int line_thickness) {
+  assert(x_pattern_len >= 0);
+  assert(y_pattern_len >= 0);
+  assert(gap >= 0);
+  assert(line_thickness > 0);
+
+  state->y_pattern_len = y_pattern_len;
+  state->x_pattern_len = x_pattern_len;
+  state->x_pattern = x_pattern;
+  state->y_pattern = y_pattern;
+  state->gap = gap;
+  state->line_thickness = line_thickness;
+  state->output_width = x_pattern_len * gap;
+  state->output_height = y_pattern_len * gap;
+
+  state->surface = SDL_CreateRGBSurface(0, state->output_width,
+                                        state->output_height, 32, 0, 0, 0, 0);
+  if (!state->surface) {
+    return Hitomezashi_State_Init_Result_Err_Create_Surface;
+  }
+  return Hitomezashi_State_Init_Result_Success;
+}
+
+enum Hitomezashi_Draw_Result hitomezashi_draw(struct Hitomezashi_State *state) {
+  if (SDL_LockSurface(state->surface) != 0) {
+    return Hitomezashi_Draw_Result_Err_Lock_Surface;
+  }
+
+  Uint32 bg_colour =
+      SDL_MapRGB(state->surface->format, HITOMEZASHI_BG_COLOUR.r,
+                 HITOMEZASHI_BG_COLOUR.g, HITOMEZASHI_BG_COLOUR.b);
+  Uint32 fg_colour =
+      SDL_MapRGB(state->surface->format, HITOMEZASHI_FG_COLOUR.r,
+                 HITOMEZASHI_FG_COLOUR.g, HITOMEZASHI_FG_COLOUR.b);
+
+  SDL_FillRect(state->surface, NULL, bg_colour);
+
+  SDL_Rect rect;
+  // Draw y pattern (horizontal) lines
+  for (int i = 0; i < state->y_pattern_len; ++i) {
+    for (int j = 0; j < state->x_pattern_len; ++j) {
+      if (j % 2 == state->y_pattern[i]) {
+        rect.x = j * state->gap;
+        rect.y = i * state->gap;
+        rect.w = state->gap;
+        rect.h = state->line_thickness;
+        SDL_FillRect(state->surface, &rect, fg_colour);
+      }
+    }
+  }
+  // Draw x pattern (vertical) lines
+  for (int i = 0; i < state->x_pattern_len; ++i) {
+    for (int j = 0; j < state->y_pattern_len; ++j) {
+      if (j % 2 == state->x_pattern[i]) {
+        rect.x = i * state->gap;
+        rect.y = j * state->gap;
+        rect.w = state->line_thickness;
+        rect.h = state->gap;
+        SDL_FillRect(state->surface, &rect, fg_colour);
+      }
+    }
+  }
+  // Join up the lines to avoid leaving holes at the intersections
+  for (int x = state->gap; x < state->output_width; x += state->gap) {
+    for (int y = state->gap; y < state->output_height; y += state->gap) {
+      rect.x = x;
+      rect.y = y;
+      rect.w = state->line_thickness;
+      rect.h = state->line_thickness;
+      SDL_FillRect(state->surface, &rect, fg_colour);
+    }
+  }
+
+  SDL_UnlockSurface(state->surface);
+  return Hitomezashi_Draw_Result_Success;
+}