avfilter/avf_showcqt: render default font at 960x16

and let ffmpeg scaler scale it
this impoves quality
Signed-off-by: Muhammad Faiz <mfcc64@gmail.com>

libavfilter/avf_showcqt.c

@@ -434,14 +434,16 @@ static double b_func(void *p, double x)
     return lrint(x*255.0);
 }
 
-static int init_axis_color(ShowCQTContext *s, AVFrame *tmp)
+static int init_axis_color(ShowCQTContext *s, AVFrame *tmp, int half)
 {
     const char *var_names[] = { "timeclamp", "tc", "frequency", "freq", "f", NULL };
     const char *func_names[] = { "midi", "r", "g", "b", NULL };
     double (*funcs[])(void *, double) = { midi, r_func, g_func, b_func };
     AVExpr *expr = NULL;
     double *freq = NULL;
-    int x, y, ret;
+    int x, xs, y, ret;
+    int width = half ? 1920/2 : 1920, height = half ? 16 : 32;
+    int step = half ? 2 : 1;
 
     if (s->basefreq != (double) BASEFREQ || s->endfreq != (double) ENDFREQ) {
         av_log(s->ctx, AV_LOG_WARNING, "font axis rendering is not implemented in non-default frequency range,"
@@ -460,17 +462,16 @@ static int init_axis_color(ShowCQTContext *s, AVFrame *tmp)
         return ret;
     }
 
-    for (x = 0; x < 1920; x++) {
-        double vars[] = { s->timeclamp, s->timeclamp, freq[x], freq[x], freq[x] };
+    for (x = 0, xs = 0; x < width; x++, xs += step) {
+        double vars[] = { s->timeclamp, s->timeclamp, freq[xs], freq[xs], freq[xs] };
         int color = (int) av_expr_eval(expr, vars, NULL);
         uint8_t r = (color >> 16) & 0xFF, g = (color >> 8) & 0xFF, b = color & 0xFF;
         uint8_t *data = tmp->data[0];
         int linesize = tmp->linesize[0];
-        for (y = 0; y < 32; y++) {
+        for (y = 0; y < height; y++) {
             data[linesize * y + 4 * x] = r;
             data[linesize * y + 4 * x + 1] = g;
             data[linesize * y + 4 * x + 2] = b;
-            data[linesize * y + 4 * x + 3] = 0;
         }
     }
 
@@ -570,19 +571,18 @@ static int render_default_font(AVFrame *tmp)
     int x, u, v, mask;
     uint8_t *data = tmp->data[0];
     int linesize = tmp->linesize[0];
+    int width = 1920/2, height = 16;
 
-    for (x = 0; x < 1920; x += 192) {
+    for (x = 0; x < width; x += width/10) {
         uint8_t *startptr = data + 4 * x;
         for (u = 0; u < 12; u++) {
-            for (v = 0; v < 16; v++) {
-                uint8_t *p = startptr + 2 * v * linesize + 16 * 4 * u;
-                for (mask = 0x80; mask; mask >>= 1, p += 8) {
-                    if (mask & avpriv_vga16_font[str[u] * 16 + v]) {
+            for (v = 0; v < height; v++) {
+                uint8_t *p = startptr + v * linesize + height/2 * 4 * u;
+                for (mask = 0x80; mask; mask >>= 1, p += 4) {
+                    if (mask & avpriv_vga16_font[str[u] * 16 + v])
                         p[3] = 255;
-                        p[7] = 255;
-                        p[linesize+3] = 255;
-                        p[linesize+7] = 255;
-                    }
+                    else
+                        p[3] = 0;
                 }
             }
         }
@@ -595,22 +595,27 @@ static int init_axis_from_font(ShowCQTContext *s)
 {
     AVFrame *tmp = NULL;
     int ret = AVERROR(ENOMEM);
+    int width = 1920, height = 32;
+    int default_font = 0;
 
-    if (!(tmp = alloc_frame_empty(AV_PIX_FMT_RGBA, 1920, 32)))
+    if (!(tmp = alloc_frame_empty(AV_PIX_FMT_RGBA, width, height)))
         goto fail;
 
     if (!(s->axis_frame = av_frame_alloc()))
         goto fail;
 
-    if ((ret = init_axis_color(s, tmp)) < 0)
+    if (render_freetype(s, tmp) < 0 && (default_font = 1, ret = render_default_font(tmp)) < 0)
         goto fail;
 
-    if (render_freetype(s, tmp) < 0 && (ret = render_default_font(tmp)) < 0)
+    if (default_font)
+        width /= 2, height /= 2;
+
+    if ((ret = init_axis_color(s, tmp, default_font)) < 0)
         goto fail;
 
     if ((ret = ff_scale_image(s->axis_frame->data, s->axis_frame->linesize, s->width, s->axis_h,
                               convert_axis_pixel_format(s->format), tmp->data, tmp->linesize,
-                              1920, 32, AV_PIX_FMT_RGBA, s->ctx)) < 0)
+                              width, height, AV_PIX_FMT_RGBA, s->ctx)) < 0)
         goto fail;
 
     av_frame_free(&tmp);