VSE: factor out sequencer_scopes.hh header

- RGB -> YUV conversion uses BT709 (just like image vectorscope),
  instead of "something similar but not quite".
- It now has square aspect ratio.
- Shows skin tone line, just like image vectorscope.
- Shows full saturation and "safe" saturation range as filled area,
  drawing that on the GPU instead of poking in the full saturation
  ring on the CPU into the texture.

@@ -43,0 +53,4 @@
+  blender::ed::seq::SeqScopes scopes;
+
+  SpaceSeq_Runtime() = default;
+  SpaceSeq_Runtime(const SpaceSeq_Runtime &) = delete;

@@ -0,0 +30,4 @@
+
+  void cleanup();
+
+  ImBuf *reference_ibuf = nullptr;

@@ -76,2 +75,4 @@
 typedef struct SpaceFile_Runtime SpaceFile_Runtime;
 
+/** Defined in `sequencer_intern.hh`. */
+typedef struct SpaceSeq_Runtime SpaceSeq_Runtime;

@@ -572,0 +537,4 @@
+  float grid_x_0 = area.xmin;
+  float grid_x_1 = area.xmax;
+  /* Float histograms show -0.25 .. 1.25 area horizontally. */
+  if (hist.data.size() > 256) {

@@ -613,2 +545,2 @@
-        scope = scopes->histogram_ibuf;
-        break;
+  View2D *v2d = &region->v2d;
+  const float text_scale_x = BLI_rctf_size_x(&v2d->cur) / BLI_rcti_size_x(&v2d->mask);

@@ -615,0 +553,4 @@
+
+    /* Label. */
+    char buf[10];
+    snprintf(buf, sizeof(buf), "%.2f", val);

@@ -623,0 +616,4 @@
+  for (int i = 0; i < 3; i++) {
+    const float y = area.ymin + (area.ymax - area.ymin) * lines[i];
+    char buf[10];
+    snprintf(buf, sizeof(buf), "%.1f", lines[i]);

@@ -623,0 +681,4 @@
+
+  /* skin tone line */
+  uchar col_tone[4] = {255, 102, 0, 128};
+  const float tone_line_len = 0.895f; /* makes it end at outer edge of saturation ring */

@@ -623,0 +698,4 @@
+  sequencer_preview_get_rect(&preview, scene, region, sseq, draw_overlay, false);
+
+  rctf uv;
+  if (draw_overlay && (sseq->overlay_frame_type == SEQ_OVERLAY_FRAME_TYPE_RECT)) {

@@ -566,4 +284,3 @@
     return 511;
   }
-
   return int(((f + 0.25f) / 1.5f) * 512);