[Mesa-dev] [PATCH v2 1/2] r600: correct texture offset for array index lookup

[Gert Wollny]

For texture array lookup the slice index is evaluated according to
  idx = floor(z + 0.5)

This patch implements the first part by adding 0.5 to the according
texture coordinate when appropriate.

Fixes multi-sample tests out of:
  dEQP-GLES3.functional.texture.shadow.2d_array.*
  dEQP-GLES3.functional.texture.vertex.2d_array.*
  dEQP-GLES3.functional.texture.filtering.2d_array.*
(In the multi-sample case the rounding accuracy is not tested.)

v2: - Don't apply texture offset correction for GATHER*O (corrects piglit
      failures reported by Dave Airlie)
    - unconditionally set the texture offset to 1 (=0.5) because the shader
      can't set an offset for the array index (Roland Scheidegger)
    - Add Fixes comment to commit message

Signed-off-by: Gert Wollny <gert.wollny at collabora.com>
---
 src/gallium/drivers/r600/r600_shader.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/gallium/drivers/r600/r600_shader.c b/src/gallium/drivers/r600/r600_shader.c
index c466a48262..4d17b3d875 100644
--- a/src/gallium/drivers/r600/r600_shader.c
+++ b/src/gallium/drivers/r600/r600_shader.c
@@ -7456,6 +7456,7 @@ static int tgsi_tex(struct r600_shader_ctx *ctx)
 	int8_t offset_x = 0, offset_y = 0, offset_z = 0;
 	boolean has_txq_cube_array_z = false;
 	unsigned sampler_index_mode;
+	int *array_index_offset = NULL;
 
 	if (inst->Instruction.Opcode == TGSI_OPCODE_TXQ &&
 	    ((inst->Texture.Texture == TGSI_TEXTURE_CUBE_ARRAY ||
@@ -8411,18 +8412,33 @@ static int tgsi_tex(struct r600_shader_ctx *ctx)
 		    opcode == FETCH_OP_SAMPLE_C_LB) {
 			/* the array index is read from Y */
 			tex.coord_type_y = 0;
+			array_index_offset = &tex.offset_y;
 		} else {
 			/* the array index is read from Z */
 			tex.coord_type_z = 0;
 			tex.src_sel_z = tex.src_sel_y;
+			array_index_offset = &tex.offset_z;
+
 		}
 	} else if (inst->Texture.Texture == TGSI_TEXTURE_2D_ARRAY ||
 		   inst->Texture.Texture == TGSI_TEXTURE_SHADOW2D_ARRAY ||
 		   ((inst->Texture.Texture == TGSI_TEXTURE_CUBE_ARRAY ||
 		    inst->Texture.Texture == TGSI_TEXTURE_SHADOWCUBE_ARRAY) &&
-		    (ctx->bc->chip_class >= EVERGREEN)))
+		    (ctx->bc->chip_class >= EVERGREEN))) {
 		/* the array index is read from Z */
 		tex.coord_type_z = 0;
+		array_index_offset = &tex.offset_z;
+	}
+
+	/* We have array access, the coordinates are not int and we use the
+	 * offset registers -> add 0.5 to the array index to adjust it according
+	 * to floor(z + 0.5). The floor opretaion is set as TRUNC in the texture
+	 * state.
+	 */
+	if (array_index_offset && opcode != FETCH_OP_LD &&
+	    opcode != FETCH_OP_GATHER4_C_O && opcode != FETCH_OP_GATHER4_O) {
+		*array_index_offset = 1;
+	}
 
 	/* mask unused source components */
 	if (opcode == FETCH_OP_SAMPLE || opcode == FETCH_OP_GATHER4) {
-- 
2.16.4