Am Freitag, den 23.06.2017, 11:17 +0200 schrieb Philipp Zabel:
> Before resolving a rendertarget or a depth/stencil resource into a
> texture, flush both the color cache and the depth cache together.
>
> It is unclear whether this is necessary for the following stall to
> work properly, or whether the depth flush just adds enough time
> for the color cache flush to finish before the resolver is started,
> but this change removes artifacts that otherwise appear if a texture
> is sampled directly after rendering into it.
>
> The test case is a simple QML scene graph with a QtWebEngine based
> WebView rendered on top of a blue background:
>
> import QtQuick 2.0
> import QtQuick.Window 2.2
> import QtWebView 1.1
>
> Window {
> Rectangle {
> id: background
> anchors.fill: parent
> color: "blue"
> }
>
> WebView {
> id: webView
> anchors.fill: parent
> }
>
> Component.onCompleted: {
> webView.url = "<some animated website>"
> }
> }
>
> If the website is animated, the WebView renders the site contents into
> texture tiles and immediately afterwards samples from them to draw the
> tiles into the Qt renderbuffer. Without this patch, a small irregular
> triangle in the lower right of each browser tile appears solid blue, as
> if the texture sampler samples zeroes instead of the website contents,
> and the previously rendered blue Rectangle shows through.
>
> Other attempts such as adding a pipeline stall before the color flush or
> a TS cache flush afterwards or flushing multiple times, with stalls
> before and after each flush, have shown no effect.
>
> Signed-off-by: Philipp Zabel <p.za...@pengutronix.de>
> ---
> Changes since v1:
> - Add a comment explaining why we flush color and depth cache together.
If there are no objections, I'm going to push this change before the
17.2 branchpoint, as it fixes a real bug, even though we don't fully
understand why this is needed.
Regards,
Lucas
> ---
> src/gallium/drivers/etnaviv/etnaviv_clear_blit.c | 22 +++++++++++++---------
> 1 file changed, 13 insertions(+), 9 deletions(-)
>
> diff --git a/src/gallium/drivers/etnaviv/etnaviv_clear_blit.c
> b/src/gallium/drivers/etnaviv/etnaviv_clear_blit.c
> index e4620a3015..d9538907fe 100644
> --- a/src/gallium/drivers/etnaviv/etnaviv_clear_blit.c
> +++ b/src/gallium/drivers/etnaviv/etnaviv_clear_blit.c
> @@ -465,15 +465,19 @@ etna_try_rs_blit(struct pipe_context *pctx,
> ts_mem_config |= VIVS_TS_MEM_CONFIG_MSAA | msaa_format;
> }
>
> - uint32_t to_flush = 0;
> -
> - if (src->base.bind & PIPE_BIND_RENDER_TARGET)
> - to_flush |= VIVS_GL_FLUSH_CACHE_COLOR;
> - if (src->base.bind & PIPE_BIND_DEPTH_STENCIL)
> - to_flush |= VIVS_GL_FLUSH_CACHE_DEPTH;
> -
> - if (to_flush) {
> - etna_set_state(ctx->stream, VIVS_GL_FLUSH_CACHE, to_flush);
> + /* Always flush color and depth cache together before resolving. This
> works
> + * around artifacts that appear in some cases when scanning out a texture
> + * directly after it has been rendered to, such as rendering an animated
> web
> + * page in a QtWebEngine based WebView on GC2000. The artifacts look like
> + * the texture sampler samples zeroes instead of texture data in a small,
> + * irregular triangle in the lower right of each browser tile quad. Other
> + * attempts to avoid these artifacts, including a pipeline stall before
> the
> + * color flush or a TS cache flush afterwards, or flushing multiple times,
> + * with stalls before and after each flush, have shown no effect. */
> + if (src->base.bind & PIPE_BIND_RENDER_TARGET ||
> + src->base.bind & PIPE_BIND_DEPTH_STENCIL) {
> + etna_set_state(ctx->stream, VIVS_GL_FLUSH_CACHE,
> + VIVS_GL_FLUSH_CACHE_COLOR | VIVS_GL_FLUSH_CACHE_DEPTH);
> etna_stall(ctx->stream, SYNC_RECIPIENT_RA, SYNC_RECIPIENT_PE);
> }
>
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