broke out background-clearing code from base overlay primitive

overviewer_core/src/primitives/clear-base.c

@@ -0,0 +1,49 @@
+/* 
+ * This file is part of the Minecraft Overviewer.
+ *
+ * Minecraft Overviewer is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * Minecraft Overviewer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General
+ * Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with the Overviewer.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "../overviewer.h"
+
+static int
+clear_base_occluded(void *data, RenderState *state, int x, int y, int z) {
+    if ( (x != 0) && (y != 15) && (z != 127) &&
+         !render_mode_hidden(state->rendermode, x-1, y, z) &&
+         !render_mode_hidden(state->rendermode, x, y, z+1) &&
+         !render_mode_hidden(state->rendermode, x, y+1, z) &&
+         !is_transparent(getArrayByte3D(state->blocks, x-1, y, z)) &&
+         !is_transparent(getArrayByte3D(state->blocks, x, y, z+1)) &&
+         !is_transparent(getArrayByte3D(state->blocks, x, y+1, z))) {
+        return 1;
+    }
+    
+    return 0;
+}
+
+static void
+clear_base_draw(void *data, RenderState *state, PyObject *src, PyObject *mask, PyObject *mask_light) {
+    /* clear the draw space -- set alpha to 0 within mask */
+    tint_with_mask(state->img, 255, 255, 255, 0, mask, state->imgx, state->imgy, 0, 0);
+}
+
+RenderPrimitiveInterface primitive_clear_base = {
+    "clear-base",
+    0,
+    NULL,
+    NULL,
+    clear_base_occluded,
+    NULL,
+    clear_base_draw,
+};