lavfi/opencl: Use filter device if no input device is available

This allows implementing sources as well as filters.

libavfilter/opencl.c

@@ -42,11 +42,29 @@ int ff_opencl_filter_query_formats(AVFilterContext *avctx)
     return ff_set_common_formats(avctx, formats);
 }
 
+static int opencl_filter_set_device(AVFilterContext *avctx,
+                                    AVBufferRef *device)
+{
+    OpenCLFilterContext *ctx = avctx->priv;
+
+    av_buffer_unref(&ctx->device_ref);
+
+    ctx->device_ref = av_buffer_ref(device);
+    if (!ctx->device_ref)
+        return AVERROR(ENOMEM);
+
+    ctx->device = (AVHWDeviceContext*)ctx->device_ref->data;
+    ctx->hwctx  = ctx->device->hwctx;
+
+    return 0;
+}
+
 int ff_opencl_filter_config_input(AVFilterLink *inlink)
 {
     AVFilterContext   *avctx = inlink->dst;
     OpenCLFilterContext *ctx = avctx->priv;
     AVHWFramesContext *input_frames;
+    int err;
 
     if (!inlink->hw_frames_ctx) {
         av_log(avctx, AV_LOG_ERROR, "OpenCL filtering requires a "
@@ -59,15 +77,12 @@ int ff_opencl_filter_config_input(AVFilterLink *inlink)
         return 0;
 
     input_frames = (AVHWFramesContext*)inlink->hw_frames_ctx->data;
-
     if (input_frames->format != AV_PIX_FMT_OPENCL)
         return AVERROR(EINVAL);
 
-    ctx->device_ref = av_buffer_ref(input_frames->device_ref);
-    if (!ctx->device_ref)
-        return AVERROR(ENOMEM);
-    ctx->device = input_frames->device_ctx;
-    ctx->hwctx  = ctx->device->hwctx;
+    err = opencl_filter_set_device(avctx, input_frames->device_ref);
+    if (err < 0)
+        return err;
 
     // Default output parameters match input parameters.
     if (ctx->output_format == AV_PIX_FMT_NONE)
@@ -90,6 +105,18 @@ int ff_opencl_filter_config_output(AVFilterLink *outlink)
 
     av_buffer_unref(&outlink->hw_frames_ctx);
 
+    if (!ctx->device_ref) {
+        if (!avctx->hw_device_ctx) {
+            av_log(avctx, AV_LOG_ERROR, "OpenCL filtering requires an "
+                   "OpenCL device.\n");
+            return AVERROR(EINVAL);
+        }
+
+        err = opencl_filter_set_device(avctx, avctx->hw_device_ctx);
+        if (err < 0)
+            return err;
+    }
+
     output_frames_ref = av_hwframe_ctx_alloc(ctx->device_ref);
     if (!output_frames_ref) {
         err = AVERROR(ENOMEM);