gl: upload: Implement the fixate_caps virtual function

We now prefer the 2D target than other targets when fixating src caps.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5468>

girs/GstGL-1.0.gir

@@ -7385,6 +7385,32 @@ A #GstGLUpload can be created with gst_gl_upload_new()</doc>
           <type name="Gst.Caps" c:type="GstCaps*"/>
         </return-value>
       </function>
+      <method name="fixate_caps" c:identifier="gst_gl_upload_fixate_caps" version="1.24">
+        <doc xml:space="preserve" filename="../subprojects/gst-plugins-base/gst-libs/gst/gl/gstglupload.c">Fixate the @othercaps based on the information of the @caps.</doc>
+        <source-position filename="../subprojects/gst-plugins-base/gst-libs/gst/gl/gstglupload.h"/>
+        <return-value transfer-ownership="full">
+          <doc xml:space="preserve" filename="../subprojects/gst-plugins-base/gst-libs/gst/gl/gstglupload.c">the fixated caps</doc>
+          <type name="Gst.Caps" c:type="GstCaps*"/>
+        </return-value>
+        <parameters>
+          <instance-parameter name="upload" transfer-ownership="none">
+            <doc xml:space="preserve" filename="../subprojects/gst-plugins-base/gst-libs/gst/gl/gstglupload.c">a #GstGLUpload</doc>
+            <type name="GLUpload" c:type="GstGLUpload*"/>
+          </instance-parameter>
+          <parameter name="direction" transfer-ownership="none">
+            <doc xml:space="preserve" filename="../subprojects/gst-plugins-base/gst-libs/gst/gl/gstglupload.c">the pad #GstPadDirection</doc>
+            <type name="Gst.PadDirection" c:type="GstPadDirection"/>
+          </parameter>
+          <parameter name="caps" transfer-ownership="none">
+            <doc xml:space="preserve" filename="../subprojects/gst-plugins-base/gst-libs/gst/gl/gstglupload.c">a #GstCaps as the reference</doc>
+            <type name="Gst.Caps" c:type="GstCaps*"/>
+          </parameter>
+          <parameter name="othercaps" transfer-ownership="full">
+            <doc xml:space="preserve" filename="../subprojects/gst-plugins-base/gst-libs/gst/gl/gstglupload.c">a #GstCaps to fixate</doc>
+            <type name="Gst.Caps" c:type="GstCaps*"/>
+          </parameter>
+        </parameters>
+      </method>
       <method name="get_caps" c:identifier="gst_gl_upload_get_caps">
         <source-position filename="../subprojects/gst-plugins-base/gst-libs/gst/gl/gstglupload.h"/>
         <return-value transfer-ownership="none">

subprojects/gst-plugins-base/ext/gl/gstgluploadelement.c

@@ -58,11 +58,12 @@ gst_gl_upload_element_prepare_output_buffer (GstBaseTransform * bt,
 static GstFlowReturn gst_gl_upload_element_transform (GstBaseTransform * bt,
     GstBuffer * buffer, GstBuffer * outbuf);
 static gboolean gst_gl_upload_element_stop (GstBaseTransform * bt);
+static GstCaps *gst_gl_upload_element_fixate_caps (GstBaseTransform * bt,
+    GstPadDirection direction, GstCaps * caps, GstCaps * othercaps);
 static GstStateChangeReturn
 gst_gl_upload_element_change_state (GstElement * element,
     GstStateChange transition);
 
-
 static GstStaticPadTemplate gst_gl_upload_element_src_pad_template =
 GST_STATIC_PAD_TEMPLATE ("src",
     GST_PAD_SRC,
@@ -110,6 +111,7 @@ gst_gl_upload_element_class_init (GstGLUploadElementClass * klass)
   bt_class->prepare_output_buffer = gst_gl_upload_element_prepare_output_buffer;
   bt_class->transform = gst_gl_upload_element_transform;
   bt_class->stop = gst_gl_upload_element_stop;
+  bt_class->fixate_caps = gst_gl_upload_element_fixate_caps;
 
   element_class->change_state = gst_gl_upload_element_change_state;
 
@@ -331,6 +333,15 @@ gst_gl_upload_element_transform (GstBaseTransform * bt, GstBuffer * buffer,
   return GST_FLOW_OK;
 }
 
+static GstCaps *
+gst_gl_upload_element_fixate_caps (GstBaseTransform * bt,
+    GstPadDirection direction, GstCaps * caps, GstCaps * othercaps)
+{
+  GstGLUploadElement *upload = GST_GL_UPLOAD_ELEMENT (bt);
+
+  return gst_gl_upload_fixate_caps (upload->upload, direction, caps, othercaps);
+}
+
 static GstStateChangeReturn
 gst_gl_upload_element_change_state (GstElement * element,
     GstStateChange transition)

subprojects/gst-plugins-base/gst-libs/gst/gl/gstglupload.c

@@ -3526,3 +3526,74 @@ restart:
 
 #undef NEXT_METHOD
 }
+
+/**
+ * gst_gl_upload_fixate_caps:
+ * @upload: a #GstGLUpload
+ * @direction: the pad #GstPadDirection
+ * @caps: a #GstCaps as the reference
+ * @othercaps: (transfer full): a #GstCaps to fixate
+ *
+ * Fixate the @othercaps based on the information of the @caps.
+ *
+ * Returns: (transfer full): the fixated caps
+ *
+ * Since: 1.24
+ */
+GstCaps *
+gst_gl_upload_fixate_caps (GstGLUpload * upload, GstPadDirection direction,
+    GstCaps * caps, GstCaps * othercaps)
+{
+  guint n, i;
+  GstGLTextureTarget target;
+  GstCaps *ret_caps = NULL;
+
+  GST_DEBUG_OBJECT (upload, "Fixate caps %" GST_PTR_FORMAT ", using caps %"
+      GST_PTR_FORMAT ", direction is %s.", othercaps, caps,
+      direction == GST_PAD_SRC ? "src" : "sink");
+
+  if (direction == GST_PAD_SRC) {
+    ret_caps = gst_caps_fixate (othercaps);
+    goto out;
+  }
+
+  if (gst_caps_is_fixed (othercaps)) {
+    ret_caps = othercaps;
+    goto out;
+  }
+
+  /* Prefer target 2D->rectangle->oes */
+  for (target = GST_GL_TEXTURE_TARGET_2D;
+      target <= GST_GL_TEXTURE_TARGET_EXTERNAL_OES; target++) {
+    n = gst_caps_get_size (othercaps);
+    for (i = 0; i < n; i++) {
+      GstStructure *s;
+
+      s = gst_caps_get_structure (othercaps, i);
+      if (_structure_check_target (s, 1 << target))
+        break;
+    }
+
+    /* If the target is found, fixate the other fields */
+    if (i < n) {
+      ret_caps = gst_caps_new_empty ();
+      gst_caps_append_structure_full (ret_caps,
+          gst_structure_copy (gst_caps_get_structure (othercaps, i)),
+          gst_caps_features_copy (gst_caps_get_features (othercaps, i)));
+
+      ret_caps = gst_caps_fixate (ret_caps);
+      gst_caps_set_simple (ret_caps, "texture-target", G_TYPE_STRING,
+          gst_gl_texture_target_to_string (target), NULL);
+
+      gst_caps_unref (othercaps);
+
+      goto out;
+    }
+  }
+
+  ret_caps = gst_caps_fixate (othercaps);
+
+out:
+  GST_DEBUG_OBJECT (upload, "Fixate return %" GST_PTR_FORMAT, ret_caps);
+  return ret_caps;
+}

subprojects/gst-plugins-base/gst-libs/gst/gl/gstglupload.h

@@ -119,6 +119,12 @@ GstGLUploadReturn gst_gl_upload_perform_with_buffer (GstGLUpload * upload,
                                                     GstBuffer * buffer,
                                                     GstBuffer ** outbuf_ptr);
 
+GST_GL_API
+GstCaps *     gst_gl_upload_fixate_caps            (GstGLUpload * upload,
+                                                    GstPadDirection direction,
+                                                    GstCaps * caps,
+                                                    GstCaps * othercaps);
+
 G_END_DECLS
 
 #endif /* __GST_GL_UPLOAD_H__ */