[Mesa-dev] [PATCH] i965: do not round line width when multisampling or antialiasing are enabled

[Iago Toral Quiroga]

In commit fe74fee8fa721a we rounded the line width to the nearest integer to
match the GLES3 spec requirements stated in section 13.4.2.1, but that seems
to break a dEQP test that renders wide lines in some multisampling scenarios.

Ian noted that the Open 4.4 spec has the following similar text:

    "The actual width of non-antialiased lines is determined by rounding the
    supplied width to the nearest integer, then clamping it to the
    implementation-dependent maximum non-antialiased line width."

and suggested that when ES removed antialiased lines, they removed
"non-antialised" from that paragraph but probably should not have.

Going by that note, this patch restricts the quantization implemented in
fe74fee8fa721a only to regular aliased lines. This seems to fix the broken
test without causing regressions in any of the dEQP line rasterization tests
(dEQP-GLES3.functional.rasterization.*line*).

Fixes:
dEQP-GLES3.functional.rasterization.fbo.rbo_multisample_max.primitives.lines_wide

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90749
---
 src/mesa/drivers/dri/i965/gen6_sf_state.c | 5 +++--
 src/mesa/drivers/dri/i965/gen7_sf_state.c | 6 ++++--
 src/mesa/drivers/dri/i965/gen8_sf_state.c | 5 +++--
 3 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/gen6_sf_state.c b/src/mesa/drivers/dri/i965/gen6_sf_state.c
index e445ce2..b674268 100644
--- a/src/mesa/drivers/dri/i965/gen6_sf_state.c
+++ b/src/mesa/drivers/dri/i965/gen6_sf_state.c
@@ -364,8 +364,9 @@ upload_sf_state(struct brw_context *brw)
       /* OpenGL dictates that line width should be rounded to the nearest
        * integer
        */
-      float line_width =
-         roundf(CLAMP(ctx->Line.Width, 0.0, ctx->Const.MaxLineWidth));
+      float line_width = CLAMP(ctx->Line.Width, 0.0, ctx->Const.MaxLineWidth);
+      if (!ctx->Multisample._Enabled && !ctx->Line.SmoothFlag)
+         line_width = CLAMP(roundf(line_width), 0.0, ctx->Const.MaxLineWidth);
       uint32_t line_width_u3_7 = U_FIXED(line_width, 7);
 
       /* Line width of 0 is not allowed when MSAA enabled */
diff --git a/src/mesa/drivers/dri/i965/gen7_sf_state.c b/src/mesa/drivers/dri/i965/gen7_sf_state.c
index 58e3337..07b4394 100644
--- a/src/mesa/drivers/dri/i965/gen7_sf_state.c
+++ b/src/mesa/drivers/dri/i965/gen7_sf_state.c
@@ -195,9 +195,11 @@ upload_sf_state(struct brw_context *brw)
       /* OpenGL dictates that line width should be rounded to the nearest
        * integer
        */
-      float line_width =
-         roundf(CLAMP(ctx->Line.Width, 0.0, ctx->Const.MaxLineWidth));
+      float line_width = CLAMP(ctx->Line.Width, 0.0, ctx->Const.MaxLineWidth);
+      if (!ctx->Multisample._Enabled && !ctx->Line.SmoothFlag)
+         line_width = CLAMP(roundf(line_width), 0.0, ctx->Const.MaxLineWidth);
       uint32_t line_width_u3_7 = U_FIXED(line_width, 7);
+
       /* Line width of 0 is not allowed when MSAA enabled */
       if (ctx->Multisample._Enabled) {
          if (line_width_u3_7 == 0)
diff --git a/src/mesa/drivers/dri/i965/gen8_sf_state.c b/src/mesa/drivers/dri/i965/gen8_sf_state.c
index 52a21b6..6c765f0 100644
--- a/src/mesa/drivers/dri/i965/gen8_sf_state.c
+++ b/src/mesa/drivers/dri/i965/gen8_sf_state.c
@@ -157,8 +157,9 @@ upload_sf(struct brw_context *brw)
    /* OpenGL dictates that line width should be rounded to the nearest
     * integer
     */
-   float line_width =
-      roundf(CLAMP(ctx->Line.Width, 0.0, ctx->Const.MaxLineWidth));
+   float line_width = CLAMP(ctx->Line.Width, 0.0, ctx->Const.MaxLineWidth);
+   if (!ctx->Multisample._Enabled && !ctx->Line.SmoothFlag)
+      line_width = CLAMP(roundf(line_width), 0.0, ctx->Const.MaxLineWidth);
    uint32_t line_width_u3_7 = U_FIXED(line_width, 7);
    if (line_width_u3_7 == 0)
       line_width_u3_7 = 1;
-- 
2.1.0