From 1a20e38ccfdc581a158a3e9f96e25465f2ab55df Mon Sep 17 00:00:00 2001 From: Ben Widawsky Date: Wed, 2 Jul 2014 17:07:34 -0700 Subject: [PATCH] i965: Simplify viewport extents programming on GEN8 Viewport extents are a 3rd rectangle that defines which pixels get discarded as part of the rasterization process. The actual pixels drawn to the screen are an intersection of the drawing rectangle, the viewport extents, and the scissor rectangle. It permits the use of guardband clipping in all cases (see later patch). The actual pixels drawn to the screen are an intersection of the drawing rectangle, the viewport extents, and the scissor rectangle. Scissor rectangle is not super important for this discussion as it should always help do the right thing provided the programmer uses it. switch (viewport dimensions, drawrect dimension) { case viewport > drawing rectangle: no effects; break; case viewport == drawing rectangle: no effects; break; case viewport < drawing rectangle: Pixels (after the viewport transformation but before expensive rastersizing and shading operations) which are outside of the viewport are discarded. } I am unable to find a test case where this improves performance, but in all my testing it doesn't hurt performance, and intuitively, it should not ever hurt performance. It also permits us to use the guardband more freely (see upcoming patch). v2: Updating commit message. v3: Commit message updates requested by Ken Reviewed-by: Kenneth Graunke --- .../drivers/dri/i965/gen8_viewport_state.c | 24 ++++++++++++------- 1 file changed, 15 insertions(+), 9 deletions(-) diff --git a/src/mesa/drivers/dri/i965/gen8_viewport_state.c b/src/mesa/drivers/dri/i965/gen8_viewport_state.c index b5171e08770..04a45300b4b 100644 --- a/src/mesa/drivers/dri/i965/gen8_viewport_state.c +++ b/src/mesa/drivers/dri/i965/gen8_viewport_state.c @@ -100,17 +100,23 @@ gen8_upload_sf_clip_viewport(struct brw_context *brw) vp[10] = -gby; /* y-min */ vp[11] = gby; /* y-max */ - /* _NEW_SCISSOR | _NEW_VIEWPORT | _NEW_BUFFERS: Screen Space Viewport */ + /* _NEW_SCISSOR | _NEW_VIEWPORT | _NEW_BUFFERS: Screen Space Viewport + * The hardware will take the intersection of the drawing rectangle, + * scissor rectangle, and the viewport extents. We don't need to be + * smart, and can therefore just program the viewport extents. + */ + float viewport_Xmax = ctx->ViewportArray[i].X + ctx->ViewportArray[i].Width; + float viewport_Ymax = ctx->ViewportArray[i].Y + ctx->ViewportArray[i].Height; if (render_to_fbo) { - vp[12] = ctx->DrawBuffer->_Xmin; - vp[13] = ctx->DrawBuffer->_Xmax - 1; - vp[14] = ctx->DrawBuffer->_Ymin; - vp[15] = ctx->DrawBuffer->_Ymax - 1; + vp[12] = ctx->ViewportArray[i].X; + vp[13] = viewport_Xmax - 1; + vp[14] = ctx->ViewportArray[i].Y; + vp[15] = viewport_Ymax - 1; } else { - vp[12] = ctx->DrawBuffer->_Xmin; - vp[13] = ctx->DrawBuffer->_Xmax - 1; - vp[14] = ctx->DrawBuffer->Height - ctx->DrawBuffer->_Ymax; - vp[15] = ctx->DrawBuffer->Height - ctx->DrawBuffer->_Ymin - 1; + vp[12] = ctx->ViewportArray[i].X; + vp[13] = viewport_Xmax - 1; + vp[14] = ctx->DrawBuffer->Height - viewport_Ymax; + vp[15] = ctx->DrawBuffer->Height - ctx->ViewportArray[i].Y - 1; } vp += 16; -- 2.30.2