vo_opengl: add a tscale=linear direct implementation

This uses GLSL mix() instead of going through an indirect texture
access. Easy to implement and might require less resources on some
devices, since the oversample code was already essentially just a
special case of this.

Could be made the new default (as per issue #2685), but that should be
done in a separate commit.

1 files changed, 10 insertions, 3 deletions

diff --git a/video/out/opengl/video.c b/video/out/opengl/video.c
index 468bee90b5..df43836c14 100644
--- a/video/out/opengl/video.c
+++ b/video/out/opengl/video.c
@@ -59,6 +59,7 @@ static const char *const fixed_scale_filters[] = {
 };
 static const char *const fixed_tscale_filters[] = {
     "oversample",
+    "linear",
     NULL
 };
 
@@ -2525,9 +2526,10 @@ static void gl_video_interpolate_frame(struct gl_video *p, struct vo_frame *t,
     struct scaler *tscale = &p->scaler[SCALER_TSCALE];
     reinit_scaler(p, tscale, &p->opts.scaler[SCALER_TSCALE], 1, tscale_sizes);
     bool oversample = strcmp(tscale->conf.kernel.name, "oversample") == 0;
+    bool linear = strcmp(tscale->conf.kernel.name, "linear") == 0;
     int size;
 
-    if (oversample) {
+    if (oversample || linear) {
         size = 2;
     } else {
         assert(tscale->kernel && !tscale->kernel->polar);
@@ -2612,8 +2614,9 @@ static void gl_video_interpolate_frame(struct gl_video *p, struct vo_frame *t,
             }
         }
 
-        // Blend the frames together
         if (oversample) {
+            // Oversample uses the frame area as mix ratio, not the the vsync
+            // position itself
             double vsync_dist = t->vsync_interval / t->ideal_frame_duration,
                    threshold = tscale->conf.kernel.params[0];
             threshold = isnan(threshold) ? 0.0 : threshold;
@@ -2621,6 +2624,10 @@ static void gl_video_interpolate_frame(struct gl_video *p, struct vo_frame *t,
             mix = mix <= 0 + threshold ? 0 : mix;
             mix = mix >= 1 - threshold ? 1 : mix;
             mix = 1 - mix;
+        }
+
+        // Blend the frames together
+        if (oversample || linear) {
             gl_sc_uniform_f(p->sc, "inter_coeff", mix);
             GLSL(color = mix(texture(texture0, texcoord0),
                              texture(texture1, texcoord1),
@@ -3489,7 +3496,7 @@ void gl_video_configure_queue(struct gl_video *p, struct vo *vo)
             radius = radius > 0 ? radius : p->opts.scaler[SCALER_TSCALE].radius;
             queue_size += 1 + ceil(radius);
         } else {
-            // Oversample case
+            // Oversample/linear case
             queue_size += 2;
         }
     }