[Mesa-dev] [PATCH] swrast: fix Z testing of points/lines for 16-bit depth buffers

[Jose Fonseca]

----- Original Message -----
> We were comparing 32-bit Z buffer values against 16-bit fragment
> values.
> Need to do scaling like for the 24-bit case.
> 
> Triangle Z testing was OK since it didn't hit this code path.
> ---
>  src/mesa/swrast/s_depth.c |   36
>  +++++++++++++++++++++++++++++-------
>  1 files changed, 29 insertions(+), 7 deletions(-)
> 
> diff --git a/src/mesa/swrast/s_depth.c b/src/mesa/swrast/s_depth.c
> index 53f21cb..42724c7 100644
> --- a/src/mesa/swrast/s_depth.c
> +++ b/src/mesa/swrast/s_depth.c
> @@ -205,6 +205,7 @@ _swrast_depth_clamp_span( struct gl_context *ctx,
> SWspan *span )
>  
>  /**
>   * Get array of 32-bit z values from the depth buffer.  With
>   clipping.
> + * Note: the returned values are always in the range [0, 2^32-1].
>   */
>  static void
>  get_z32_values(struct gl_context *ctx, struct gl_renderbuffer *rb,
> @@ -235,6 +236,11 @@ get_z32_values(struct gl_context *ctx, struct
> gl_renderbuffer *rb,
>     }
>  }
>  
> +
> +/**
> + * Put an array of 32-bit z values into the depth buffer.
> + * Note: the z values are always in the range [0, 2^32-1].
> + */
>  static void
>  put_z32_values(struct gl_context *ctx, struct gl_renderbuffer *rb,
>                 GLuint count, const GLint x[], const GLint y[],
> @@ -284,8 +290,8 @@ _swrast_depth_test_span(struct gl_context *ctx,
> SWspan *span)
>     void *zBufferVals;
>     GLuint *zBufferTemp = NULL;
>     GLuint passed;
> +   GLuint zBits = _mesa_get_format_bits(rb->Format, GL_DEPTH_BITS);
>     GLboolean ztest16 = GL_FALSE;

is ztest16 still necessary?

Otherwise looks good.

Jose

> -   GLboolean ztest24 = _mesa_get_format_bits(rb->Format,
> GL_DEPTH_BITS) == 24;
>  
>     if (rb->Format == MESA_FORMAT_Z16 && !(span->arrayMask &
>     SPAN_XY)) {
>        /* directly read/write row of 16-bit Z values */
> @@ -310,7 +316,7 @@ _swrast_depth_test_span(struct gl_context *ctx,
> SWspan *span)
>           _mesa_unpack_uint_z_row(rb->Format, count, zStart,
>           zBufferTemp);
>        }
>  
> -      if (ztest24) {
> +      if (zBits == 24) {
>           GLuint i;
>           /* Convert depth buffer values from 32 to 24 bits to match
>           the
>            * fragment Z values generated by rasterization.
> @@ -319,6 +325,16 @@ _swrast_depth_test_span(struct gl_context *ctx,
> SWspan *span)
>              zBufferTemp[i] >>= 8;
>           }
>        }
> +      else if (zBits == 16) {
> +         GLuint i;
> +         /* Convert depth buffer values from 32 to 16 bits */
> +         for (i = 0; i < count; i++) {
> +            zBufferTemp[i] >>= 16;
> +         }
> +      }
> +      else {
> +         assert(zBits == 32);
> +      }
>  
>        zBufferVals = zBufferTemp;
>     }
> @@ -332,16 +348,22 @@ _swrast_depth_test_span(struct gl_context *ctx,
> SWspan *span)
>     if (zBufferTemp) {
>        /* need to write temp Z values back into the buffer */
>  
> -      if (ztest24) {
> +      /* Convert depth buffer values back to 32-bit values.  The
> least
> +       * significant bits don't matter since they'll get dropped
> when
> +       * they're packed back into the depth buffer.
> +       */
> +      if (zBits == 24) {
>           GLuint i;
> -         /* Convert depth buffer values back to 32-bit values.  The
> least
> -          * significant bits don't matter since they'll get dropped
> when
> -          * they're packed back into the depth buffer.
> -          */
>           for (i = 0; i < count; i++) {
>              zBufferTemp[i] = (zBufferTemp[i] << 8);
>           }
>        }
> +      else if (zBits == 16) {
> +         GLuint i;
> +         for (i = 0; i < count; i++) {
> +            zBufferTemp[i] = zBufferTemp[i] << 16;
> +         }
> +      }
>  
>        if (span->arrayMask & SPAN_XY) {
>           /* random locations */
> --
> 1.7.3.4
> 
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