more faster

pixelflut.h

@@ -0,0 +1,55 @@
+/*
+ * Pixelflut binary UDP protocol, shared by the renderer and the benchmark.
+ *
+ * Packet layout (little-endian on the wire):
+ *
+ *   +------+---------+  pixelflut_packet
+ *   | cmd  | subcmd  |  2-byte header
+ *   +------+---------+---------+----+----+----+  pixelflut_pixel[0]
+ *   |   x (u16)      | y (u16) | r  | g  | b  |  7 bytes
+ *   +----------------+---------+----+----+----+
+ *   |                   ...                   |  PIXELS_PER_PACKET pixels
+ *   +----------------------------------------+
+ */
+
+#ifndef PIXELFLUT_H
+#define PIXELFLUT_H
+
+#include <stdint.h>
+
+/* Header bytes. */
+#define PIXELFLUT_CMD_SET    0x00 /* "set pixels" command ... */
+#define PIXELFLUT_SUBCMD_RGB 0x01 /* ... with 3-byte RGB colours */
+
+/* Pixels batched into a single UDP datagram. Bigger datagrams amortize the
+ * per-message send cost over more pixels; keep the packet within the path MTU
+ * to avoid IP fragmentation (e.g. 207 pixels ~= 1451 B fits a 1500 B link).
+ * Override at build time with -DPIXELS_PER_PACKET=N. */
+#ifndef PIXELS_PER_PACKET
+#  define PIXELS_PER_PACKET 120
+#endif
+
+#pragma pack(push, 1)
+/* A single pixel as it appears on the wire. */
+struct pixelflut_pixel {
+	uint16_t x; /* little-endian */
+	uint16_t y; /* little-endian */
+	uint8_t r;
+	uint8_t g;
+	uint8_t b;
+};
+
+/* A full datagram: header followed by a batch of pixels. */
+struct pixelflut_packet {
+	uint8_t cmd;
+	uint8_t subcmd;
+	struct pixelflut_pixel pixels[PIXELS_PER_PACKET];
+};
+#pragma pack(pop)
+
+_Static_assert(sizeof(struct pixelflut_pixel) == 7,
+               "pixel must be exactly 7 bytes on the wire");
+_Static_assert(sizeof(struct pixelflut_packet) == 2 + 7 * PIXELS_PER_PACKET,
+               "packet must be header + PIXELS_PER_PACKET pixels, no padding");
+
+#endif /* PIXELFLUT_H */