examples: add simple visual rendering of the samples in melody.v

examples/sokol/sounds/melody.v

@@ -1,12 +1,16 @@
-import os
+import gg
+import gx
 import sokol.audio
 
-struct AContext {
+struct AppState {
 mut:
-	frame_0 int
+	gframe  int // the current graphical frame
+	frame_0 int // offset of the current audio frames, relative to the start of the music
+	frames  [2048]f32 // a copy of the last rendered audio frames
+	gg      &gg.Context // used for drawing
 }
 
-fn my_audio_stream_callback(buffer &f32, num_frames, num_channels int, mut acontext AContext) {
+fn my_audio_stream_callback(buffer &f32, num_frames, num_channels int, mut acontext AppState) {
 	mut soundbuffer := buffer
 	for frame := 0; frame < num_frames; frame++ {
 		t := int(f32(acontext.frame_0 + frame) * 0.245)
@@ -18,7 +22,9 @@ fn my_audio_stream_callback(buffer &f32, num_frames, num_channels int, mut acont
 		for ch := 0; ch < num_channels; ch++ {
 			idx := frame * num_channels + ch
 			unsafe {
-				soundbuffer[idx] = f32(byte(y) - 127) / 255.0
+				a := f32(byte(y) - 127) / 255.0
+				soundbuffer[idx] = a
+				acontext.frames[idx & 2047] = a
 			}
 		}
 	}
@@ -26,10 +32,44 @@ fn my_audio_stream_callback(buffer &f32, num_frames, num_channels int, mut acont
 }
 
 fn main() {
+	mut state := &AppState{
+		gg: 0
+	}
 	audio.setup({
 		stream_userdata_cb: my_audio_stream_callback
-		user_data: &AContext{}
+		user_data: state
 	})
-	os.input('Press Enter to exit')
+	state.gg = gg.new_context({
+		bg_color: gx.rgb(50, 50, 50)
+		width: 1024
+		height: 400
+		use_ortho: true
+		create_window: true
+		window_title: 'ByteBeat Music'
+		frame_fn: graphics_frame
+		user_data: state
+	})
+	state.gg.run()
 	audio.shutdown()
 }
+
+fn graphics_frame(mut state AppState) {
+	state.gframe++
+	state.gg.begin()
+	state.draw()
+	state.gg.end()
+}
+
+[inline]
+fn (mut state AppState) bsample(idx int) byte {
+	return byte(127 + state.frames[(state.gframe + idx) & 2047] * 128)
+}
+
+fn (mut state AppState) draw() {
+	// first, reset and setup ortho projection
+	for x in 0 .. 1024 {
+		mut y := 100 * (state.frames[2*x] + state.frames[2*x+1])
+		state.gg.draw_line(x, 200, x, 200 + y, gx.rgba(state.bsample(x), state.bsample(x + 300),
+			state.bsample(x + 700), 255))
+	}
+}