Add support for .xbm bitmap file

.xbm is easy to include in C as source file. It could be viewed
and edited directly without need to be converted between images
and C array.

src/xbm.c

@@ -0,0 +1,67 @@
+#include "xbm.h"
+#include <stdlib.h>
+#include <memory.h>
+
+#define ALIGNBIT(x) (((x % 8)>0)*8 + (x / 8) * 8)
+
+/**
+ * Draw bitmap file to fb at (col, row)
+ * if bitmap file larger than fb, it will be stripped out
+ */
+void xbm2fb(xbm_t *xbm, uint16_t *fb, int col, int row)
+{
+	int W = ALIGNBIT(xbm->w);
+	uint16_t *tmpfb = malloc(W * sizeof(uint16_t));
+	memset(tmpfb, 0, W * sizeof(uint16_t));
+
+	if ((xbm->h + row) >= 0 && col >= 0) {
+
+		for (int h = 0; h < xbm->h; h++) {
+			for (int w = 0; w < W; w++) {
+				tmpfb[w] |= ((xbm->bits[h*(W/8) + w/8] >> (w % 8)) & 0x01) 
+					<< (h+row);
+			}
+		}
+	}
+	for (int i=0; i < xbm->w; i++) {
+		fb[col+i] = tmpfb[i];
+	}
+}
+
+void xbm2fb_dirty(xbm_t *xbm, uint16_t *fb, int col, int row)
+{
+	// Byte align for xbm bytes
+	int W = ALIGNBIT(xbm->w);
+
+	for (int h = 0; h < xbm->h; h++) {
+		for (int w = 0; w < W; w++) {
+			fb[w] |= ((xbm->bits[h*(W/8) + w/8] >> (w % 8)) & 0x01) << (h+row);
+		}
+	}
+}
+
+/**
+ * Crop image horizontaly
+ * TODO: vertical crop
+ * 
+ */
+xbm_t *xbm_croph(xbm_t *xbm, xbm_t *frame, int from_row, int to_row)
+{
+	int rb = xbm->w / 8 + ((xbm->w % 8)>0); // Number of bytes in a row
+	if (to_row * rb > rb * xbm->h)
+		return NULL;
+
+	frame->bits = &xbm->bits[rb * from_row];
+	frame->w = xbm->w;
+	frame->h = to_row - from_row;
+	frame->fh = xbm->fh;
+
+	return frame;
+}
+
+xbm_t *extract_frame(xbm_t *xbm, xbm_t *frame, int frame_index)
+{
+	int from = frame_index * xbm->fh;
+	int to = from + xbm->fh;
+	return xbm_croph(xbm, frame, from, to);
+}