video: fix bogus uses of mp_image.w/width

mp_image has this confusing distinction between the w/h and width/height
fields. w/h are the actual width and height, while width/height have a
very special meaning inside the video filter code: it's the actually
allocated width, which is also used for stride padding.

Screenshot related code abused the w/h fields to store the aspect
corrected size. Some code confused the role of w/h and width/height.

Fix these issues. For aspect corrected size, display_w/h are used, while
width/height should never be used outside vf.c internals and related
code.

This also fixes an actual bug when taking screenshots of anamorphic
video with vf_screenshot, as well as using vo_image with such videos.

core/screenshot.c

@@ -238,7 +238,7 @@ static struct mp_image *add_subs(struct MPContext *mpctx,
                                  struct mp_image *image)
 {
     if (!(image->flags & MP_IMGFLAG_ALLOCATED)) {
-        struct mp_image *new_image = alloc_mpi(image->width, image->height,
+        struct mp_image *new_image = alloc_mpi(image->w, image->h,
                                                image->imgfmt);
         copy_mpi(new_image, image);
         vf_clone_mpi_attributes(new_image, image);
@@ -248,7 +248,7 @@ static struct mp_image *add_subs(struct MPContext *mpctx,
     int d_w = image->display_w ? image->display_w : image->w;
     int d_h = image->display_h ? image->display_h : image->h;
 
-    double sar = (double)image->width / image->height;
+    double sar = (double)image->w / image->h;
     double dar = (double)d_w / d_h;
     struct mp_osd_res res = {
         .w = image->w,

video/filter/vf_screenshot.c

@@ -49,8 +49,8 @@ static int config(struct vf_instance *vf,
     free_mp_image(vf->priv->image);
     vf->priv->image = new_mp_image(width, height);
     mp_image_setfmt(vf->priv->image, outfmt);
-    vf->priv->image->w = d_width;
-    vf->priv->image->h = d_height;
+    vf->priv->image->display_w = d_width;
+    vf->priv->image->display_h = d_height;
     return vf_next_config(vf,width,height,d_width,d_height,flags,outfmt);
 }
 
@@ -142,6 +142,8 @@ static int put_image(struct vf_instance *vf, mp_image_t *mpi, double pts)
         image.w = vf->priv->image->w;
         image.h = vf->priv->image->h;
         vf_clone_mpi_attributes(&image, mpi);
+        image.display_w = vf->priv->image->display_w;
+        image.display_h = vf->priv->image->display_h;
         vf->priv->image_callback(vf->priv->image_callback_ctx, &image);
         vf->priv->store_slices = 0;
     }

video/image_writer.c

@@ -102,8 +102,8 @@ static int write_lavc(struct image_writer_ctx *ctx, mp_image_t *image, FILE *fp)
         goto print_open_fail;
 
     avctx->time_base = AV_TIME_BASE_Q;
-    avctx->width = image->width;
-    avctx->height = image->height;
+    avctx->width = image->w;
+    avctx->height = image->h;
     avctx->pix_fmt = imgfmt2pixfmt(image->imgfmt);
     if (ctx->writer->lavc_codec == CODEC_ID_PNG)
         avctx->compression_level = ctx->opts->png_compression;
@@ -115,7 +115,7 @@ static int write_lavc(struct image_writer_ctx *ctx, mp_image_t *image, FILE *fp)
         goto error_exit;
     }
 
-    size_t outbuffer_size = image->width * image->height * 3 * 2;
+    size_t outbuffer_size = image->w * image->h * 3 * 2;
     outbuffer = malloc(outbuffer_size);
     if (!outbuffer)
         goto error_exit;
@@ -173,8 +173,8 @@ static int write_jpeg(struct image_writer_ctx *ctx, mp_image_t *image, FILE *fp)
     jpeg_create_compress(&cinfo);
     jpeg_stdio_dest(&cinfo, fp);
 
-    cinfo.image_width = image->width;
-    cinfo.image_height = image->height;
+    cinfo.image_width = image->w;
+    cinfo.image_height = image->h;
     cinfo.input_components = 3;
     cinfo.in_color_space = JCS_RGB;
 
@@ -182,11 +182,8 @@ static int write_jpeg(struct image_writer_ctx *ctx, mp_image_t *image, FILE *fp)
     cinfo.JFIF_major_version = 1;
     cinfo.JFIF_minor_version = 2;
     cinfo.density_unit = 1; /* 0=unknown, 1=dpi, 2=dpcm */
-    /* Image DPI is determined by Y_density, so we leave that at
-       jpeg_dpi if possible and crunch X_density instead (PAR > 1) */
-    // NOTE: write_image never passes anamorphic images currently
-    cinfo.X_density = ctx->opts->jpeg_dpi*image->width/image->w;
-    cinfo.Y_density = ctx->opts->jpeg_dpi*image->height/image->h;
+    cinfo.X_density = ctx->opts->jpeg_dpi;
+    cinfo.Y_density = ctx->opts->jpeg_dpi;
     cinfo.write_Adobe_marker = TRUE;
 
     jpeg_set_defaults(&cinfo);

video/out/vo_image.c

@@ -101,8 +101,8 @@ static uint32_t draw_image(struct vo *vo, mp_image_t *mpi)
     struct priv *p = vo->priv;
 
     mp_image_t img = *mpi;
-    img.width = p->d_width;
-    img.height = p->d_height;
+    img.display_w = p->d_width;
+    img.display_h = p->d_height;
     mp_image_set_colorspace_details(&img, &p->colorspace);
 
     void *t = talloc_new(NULL);