avfilter/vf_v360: add cylindrical equal area format

3 files changed, 129 insertions, 0 deletions

diff --git a/doc/filters.texi b/doc/filters.texi
index 67ad228d8b..13236965ce 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -20977,6 +20977,10 @@ If diagonal field of view is set it overrides horizontal and vertical field of v
 Octahedron projection.
 @end table
 
+@item cylindricalea
+Cylindrical Equal Area projection.
+@end table
+
 @item interp
 Set interpolation method.@*
 @i{Note: more complex interpolation methods require much more memory to run.}
diff --git a/libavfilter/v360.h b/libavfilter/v360.h
index 87770664a3..b8ade2591c 100644
--- a/libavfilter/v360.h
+++ b/libavfilter/v360.h
@@ -54,6 +54,7 @@ enum Projections {
     EQUISOLID,
     ORTHOGRAPHIC,
     OCTAHEDRON,
+    CYLINDRICALEA,
     NB_PROJECTIONS,
 };
 
diff --git a/libavfilter/vf_v360.c b/libavfilter/vf_v360.c
index c47a4015e8..0c47883d4d 100644
--- a/libavfilter/vf_v360.c
+++ b/libavfilter/vf_v360.c
@@ -84,6 +84,7 @@ static const AVOption v360_options[] = {
     { "equisolid", "equisolid",                                  0, AV_OPT_TYPE_CONST,  {.i64=EQUISOLID},       0,                   0, FLAGS, "in" },
     {        "og", "orthographic",                               0, AV_OPT_TYPE_CONST,  {.i64=ORTHOGRAPHIC},    0,                   0, FLAGS, "in" },
     {"octahedron", "octahedron",                                 0, AV_OPT_TYPE_CONST,  {.i64=OCTAHEDRON},      0,                   0, FLAGS, "in" },
+    {"cylindricalea", "cylindrical equal area",                  0, AV_OPT_TYPE_CONST,  {.i64=CYLINDRICALEA},   0,                   0, FLAGS, "in" },
     {    "output", "set output projection",            OFFSET(out), AV_OPT_TYPE_INT,    {.i64=CUBEMAP_3_2},     0,    NB_PROJECTIONS-1, FLAGS, "out" },
     {         "e", "equirectangular",                            0, AV_OPT_TYPE_CONST,  {.i64=EQUIRECTANGULAR}, 0,                   0, FLAGS, "out" },
     {  "equirect", "equirectangular",                            0, AV_OPT_TYPE_CONST,  {.i64=EQUIRECTANGULAR}, 0,                   0, FLAGS, "out" },
@@ -114,6 +115,7 @@ static const AVOption v360_options[] = {
     { "equisolid", "equisolid",                                  0, AV_OPT_TYPE_CONST,  {.i64=EQUISOLID},       0,                   0, FLAGS, "out" },
     {        "og", "orthographic",                               0, AV_OPT_TYPE_CONST,  {.i64=ORTHOGRAPHIC},    0,                   0, FLAGS, "out" },
     {"octahedron", "octahedron",                                 0, AV_OPT_TYPE_CONST,  {.i64=OCTAHEDRON},      0,                   0, FLAGS, "out" },
+    {"cylindricalea", "cylindrical equal area",                  0, AV_OPT_TYPE_CONST,  {.i64=CYLINDRICALEA},   0,                   0, FLAGS, "out" },
     {    "interp", "set interpolation method",      OFFSET(interp), AV_OPT_TYPE_INT,    {.i64=BILINEAR},        0, NB_INTERP_METHODS-1, FLAGS, "interp" },
     {      "near", "nearest neighbour",                          0, AV_OPT_TYPE_CONST,  {.i64=NEAREST},         0,                   0, FLAGS, "interp" },
     {   "nearest", "nearest neighbour",                          0, AV_OPT_TYPE_CONST,  {.i64=NEAREST},         0,                   0, FLAGS, "interp" },
@@ -3137,6 +3139,116 @@ static int xyz_to_cylindrical(const V360Context *s,
 }
 
 /**
+ * Prepare data for processing cylindrical equal area output format.
+ *
+ * @param ctx filter context
+ *
+ * @return error code
+ */
+static int prepare_cylindricalea_out(AVFilterContext *ctx)
+{
+    V360Context *s = ctx->priv;
+
+    s->flat_range[0] = s->h_fov * M_PI / 360.f;
+    s->flat_range[1] = s->v_fov / 180.f;
+
+    return 0;
+}
+
+/**
+ * Prepare data for processing cylindrical equal area input format.
+ *
+ * @param ctx filter context
+ *
+ * @return error code
+ */
+static int prepare_cylindricalea_in(AVFilterContext *ctx)
+{
+    V360Context *s = ctx->priv;
+
+    s->iflat_range[0] = M_PI * s->ih_fov / 360.f;
+    s->iflat_range[1] = s->iv_fov / 180.f;
+
+    return 0;
+}
+
+/**
+ * Calculate 3D coordinates on sphere for corresponding frame position in cylindrical equal area format.
+ *
+ * @param s filter private context
+ * @param i horizontal position on frame [0, width)
+ * @param j vertical position on frame [0, height)
+ * @param width frame width
+ * @param height frame height
+ * @param vec coordinates on sphere
+ */
+static int cylindricalea_to_xyz(const V360Context *s,
+                                int i, int j, int width, int height,
+                                float *vec)
+{
+    const float uf = s->flat_range[0] * ((2.f * i + 1.f) / width  - 1.f);
+    const float vf = s->flat_range[1] * ((2.f * j + 1.f) / height - 1.f);
+
+    const float phi   = uf;
+    const float theta = asinf(vf);
+
+    const float sin_phi   = sinf(phi);
+    const float cos_phi   = cosf(phi);
+    const float sin_theta = sinf(theta);
+    const float cos_theta = cosf(theta);
+
+    vec[0] = cos_theta * sin_phi;
+    vec[1] = sin_theta;
+    vec[2] = cos_theta * cos_phi;
+
+    normalize_vector(vec);
+
+    return 1;
+}
+
+/**
+ * Calculate frame position in cylindrical equal area format for corresponding 3D coordinates on sphere.
+ *
+ * @param s filter private context
+ * @param vec coordinates on sphere
+ * @param width frame width
+ * @param height frame height
+ * @param us horizontal coordinates for interpolation window
+ * @param vs vertical coordinates for interpolation window
+ * @param du horizontal relative coordinate
+ * @param dv vertical relative coordinate
+ */
+static int xyz_to_cylindricalea(const V360Context *s,
+                                const float *vec, int width, int height,
+                                int16_t us[4][4], int16_t vs[4][4], float *du, float *dv)
+{
+    const float phi   = atan2f(vec[0], vec[2]) / s->iflat_range[0];
+    const float theta = asinf(vec[1]);
+
+    const float uf = (phi + 1.f) * (width - 1) / 2.f;
+    const float vf = (sinf(theta) / s->iflat_range[1] + 1.f) * height / 2.f;
+
+    const int ui = floorf(uf);
+    const int vi = floorf(vf);
+
+    const int visible = vi >= 0 && vi < height && ui >= 0 && ui < width &&
+                        theta <=  M_PI * s->iv_fov / 180.f &&
+                        theta >= -M_PI * s->iv_fov / 180.f;
+
+    *du = uf - ui;
+    *dv = vf - vi;
+
+    for (int i = 0; i < 4; i++) {
+        for (int j = 0; j < 4; j++) {
+            us[i][j] = visible ? av_clip(ui + j - 1, 0, width  - 1) : 0;
+            vs[i][j] = visible ? av_clip(vi + i - 1, 0, height - 1) : 0;
+        }
+    }
+
+    return visible;
+}
+
+/**
  * Calculate 3D coordinates on sphere for corresponding frame position in perspective format.
  *
  * @param s filter private context
@@ -4448,6 +4560,12 @@ static int config_output(AVFilterLink *outlink)
         wf = w;
         hf = h * 2.f;
         break;
+    case CYLINDRICALEA:
+        s->in_transform = xyz_to_cylindricalea;
+        err = prepare_cylindricalea_in(ctx);
+        wf = w;
+        hf = h;
+        break;
     case TETRAHEDRON:
         s->in_transform = xyz_to_tetrahedron;
         err = 0;
@@ -4596,6 +4714,12 @@ static int config_output(AVFilterLink *outlink)
         w = lrintf(wf);
         h = lrintf(hf * 0.5f);
         break;
+    case CYLINDRICALEA:
+        s->out_transform = cylindricalea_to_xyz;
+        prepare_out = prepare_cylindricalea_out;
+        w = lrintf(wf);
+        h = lrintf(hf);
+        break;
     case PERSPECTIVE:
         s->out_transform = perspective_to_xyz;
         prepare_out = NULL;