Refactor UI code into an immediate mode style (#1)

Co-authored-by: Abdelrahman <said.abdelrahman89@gmail.com>
Reviewed-on: #1

src/ui.c

@@ -1,6 +1,139 @@
 #include "ui.h"
+#include "SDL_events.h"
+#include "aliases/aliases.h"
+#include "window.h"
 
-bool aabb(const rect_t *rect, i32 x, i32 y) {
-  return x > rect->topleft.x && x <= rect->topleft.x + rect->w &&
-         y > rect->topleft.y && y <= rect->topleft.y + rect->h;
+bool aabb(const ui_elem_t *elem, i32 x, i32 y) {
+  return x > elem->rect.topleft.x && x <= elem->rect.topleft.x + elem->rect.w &&
+         y > elem->rect.topleft.y && y <= elem->rect.topleft.y + elem->rect.h;
+}
+
+void init_ui_ctx(ui_ctx_t *ctx) {
+  *ctx = (ui_ctx_t){0};
+  ctx->hovered = -1;
+  ctx->active = -1;
+}
+
+void reset_ui_ctx(ui_ctx_t *ctx) {
+  ctx->count = 0;
+  ctx->mouse_down = false;
+  ctx->mouse_up = false;
+}
+
+void handle_ui_events(const window_t *wnd, ui_ctx_t *ctx,
+                      const SDL_Event *event) {
+  switch (event->type) {
+  case SDL_MOUSEMOTION:
+    if (wnd->id == event->motion.windowID) {
+      ctx->mouse_x = event->motion.x;
+      ctx->mouse_y = event->motion.y;
+      ctx->wnd = wnd;
+
+      break;
+    }
+  case SDL_MOUSEBUTTONDOWN:
+    if (wnd->id == event->button.windowID) {
+      ctx->mouse_x = event->button.x;
+      ctx->mouse_y = event->button.y;
+      ctx->mouse_down = true;
+      ctx->wnd = wnd;
+    }
+
+    break;
+  case SDL_MOUSEBUTTONUP:
+    if (wnd->id == event->button.windowID) {
+      ctx->mouse_x = event->button.x;
+      ctx->mouse_y = event->button.y;
+      ctx->mouse_up = true;
+      ctx->wnd = wnd;
+    }
+
+    break;
+  }
+}
+
+bool button(const window_t *wnd, ui_ctx_t *ctx, rect_t rect,
+            ui_elem_colours_t colours) {
+  if (ctx->count + 1 >= MAX_UI_ELEMENTS) {
+    return false;
+  }
+
+  ui_elem_t elem = (ui_elem_t){
+      .id = (ctx->count)++,
+      .rect = rect,
+      .type = UI_ELEM_BUTTON,
+  };
+
+  fill_rect(wnd, rect, colours.fill);
+  draw_rect(wnd, rect, colours.border);
+
+  if (wnd != ctx->wnd || (ctx->active >= 0 && ctx->active != elem.id)) {
+    return false;
+  }
+
+  if (!aabb(&elem, ctx->mouse_x, ctx->mouse_y)) {
+    return false;
+  }
+
+  ctx->hovered = elem.id;
+
+  if (ctx->mouse_down) {
+    ctx->active = elem.id;
+  }
+
+  if (ctx->mouse_up && ctx->hovered == elem.id && ctx->active == elem.id) {
+    ctx->hovered = ctx->active = -1;
+    return true;
+  }
+
+  return false;
+}
+
+rect_t node(const window_t *wnd, ui_ctx_t *ctx, rect_t rect,
+            ui_elem_colours_t colours) {
+  if (ctx->count + 1 >= MAX_UI_ELEMENTS) {
+    return (rect_t){0};
+  }
+
+  ui_elem_t elem = (ui_elem_t){
+      .id = (ctx->count)++,
+      .rect = rect,
+      .type = UI_ELEM_NODE,
+  };
+
+  fill_rect(wnd, rect, colours.fill);
+  draw_rect(wnd, rect, colours.border);
+
+  if (wnd != ctx->wnd || (ctx->active >= 0 && ctx->active != elem.id)) {
+    return rect;
+  }
+
+  if (ctx->mouse_up) {
+    ctx->hovered = ctx->active = -1;
+    ctx->rel_x = ctx->rel_y = 0;
+    return rect;
+  }
+
+  if (ctx->hovered == elem.id && ctx->active == elem.id) {
+    return (rect_t){
+        .topleft.x = ctx->mouse_x + ctx->rel_x,
+        .topleft.y = ctx->mouse_y + ctx->rel_y,
+        .w = rect.w,
+        .h = rect.h,
+    };
+  }
+
+  if (!aabb(&elem, ctx->mouse_x, ctx->mouse_y)) {
+    return rect;
+  }
+
+  ctx->hovered = elem.id;
+
+  if (ctx->mouse_down) {
+    ctx->active = elem.id;
+    ctx->rel_x = rect.topleft.x - ctx->mouse_x;
+    ctx->rel_y = rect.topleft.y - ctx->mouse_y;
+  }
+
+  return rect;
 }