}
}
+/**
+ * Count the number of trailing 1 bits in the given value. For example:
+ *
+ * count_trailing_one_bits(0) == 0
+ * count_trailing_one_bits(7) == 3
+ * count_trailing_one_bits(11) == 2
+ */
+static inline int count_trailing_one_bits(unsigned value)
+{
+#ifdef HAVE___BUILTIN_CTZ
+ return __builtin_ctz(~value);
+#else
+ return _mesa_bitcount(value & ~(value + 1));
+#endif
+}
+
+static nir_ssa_def *
+blorp_nir_manual_blend_average(nir_builder *b, nir_ssa_def *pos,
+ unsigned tex_samples,
+ enum intel_msaa_layout tex_layout,
+ enum brw_reg_type dst_type)
+{
+ /* If non-null, this is the outer-most if statement */
+ nir_if *outer_if = NULL;
+
+ nir_variable *color =
+ nir_local_variable_create(b->impl, glsl_vec4_type(), "color");
+
+ nir_ssa_def *mcs = NULL;
+ if (tex_layout == INTEL_MSAA_LAYOUT_CMS)
+ mcs = blorp_nir_txf_ms_mcs(b, pos);
+
+ /* We add together samples using a binary tree structure, e.g. for 4x MSAA:
+ *
+ * result = ((sample[0] + sample[1]) + (sample[2] + sample[3])) / 4
+ *
+ * This ensures that when all samples have the same value, no numerical
+ * precision is lost, since each addition operation always adds two equal
+ * values, and summing two equal floating point values does not lose
+ * precision.
+ *
+ * We perform this computation by treating the texture_data array as a
+ * stack and performing the following operations:
+ *
+ * - push sample 0 onto stack
+ * - push sample 1 onto stack
+ * - add top two stack entries
+ * - push sample 2 onto stack
+ * - push sample 3 onto stack
+ * - add top two stack entries
+ * - add top two stack entries
+ * - divide top stack entry by 4
+ *
+ * Note that after pushing sample i onto the stack, the number of add
+ * operations we do is equal to the number of trailing 1 bits in i. This
+ * works provided the total number of samples is a power of two, which it
+ * always is for i965.
+ *
+ * For integer formats, we replace the add operations with average
+ * operations and skip the final division.
+ */
+ nir_ssa_def *texture_data[4];
+ unsigned stack_depth = 0;
+ for (unsigned i = 0; i < tex_samples; ++i) {
+ assert(stack_depth == _mesa_bitcount(i)); /* Loop invariant */
+
+ /* Push sample i onto the stack */
+ assert(stack_depth < ARRAY_SIZE(texture_data));
+
+ nir_ssa_def *ms_pos = nir_vec3(b, nir_channel(b, pos, 0),
+ nir_channel(b, pos, 1),
+ nir_imm_int(b, i));
+ texture_data[stack_depth++] = blorp_nir_txf_ms(b, ms_pos, mcs, dst_type);
+
+ if (i == 0 && tex_layout == INTEL_MSAA_LAYOUT_CMS) {
+ /* The Ivy Bridge PRM, Vol4 Part1 p27 (Multisample Control Surface)
+ * suggests an optimization:
+ *
+ * "A simple optimization with probable large return in
+ * performance is to compare the MCS value to zero (indicating
+ * all samples are on sample slice 0), and sample only from
+ * sample slice 0 using ld2dss if MCS is zero."
+ *
+ * Note that in the case where the MCS value is zero, sampling from
+ * sample slice 0 using ld2dss and sampling from sample 0 using
+ * ld2dms are equivalent (since all samples are on sample slice 0).
+ * Since we have already sampled from sample 0, all we need to do is
+ * skip the remaining fetches and averaging if MCS is zero.
+ */
+ nir_ssa_def *mcs_zero =
+ nir_ieq(b, nir_channel(b, mcs, 0), nir_imm_int(b, 0));
+ nir_if *if_stmt = nir_if_create(b->shader);
+ if_stmt->condition = nir_src_for_ssa(mcs_zero);
+ nir_cf_node_insert(b->cursor, &if_stmt->cf_node);
+
+ b->cursor = nir_after_cf_list(&if_stmt->then_list);
+ nir_store_var(b, color, texture_data[0], 0xf);
+
+ b->cursor = nir_after_cf_list(&if_stmt->else_list);
+ outer_if = if_stmt;
+ }
+
+ for (int j = 0; j < count_trailing_one_bits(i); j++) {
+ assert(stack_depth >= 2);
+ --stack_depth;
+
+ assert(dst_type == BRW_REGISTER_TYPE_F);
+ texture_data[stack_depth - 1] =
+ nir_fadd(b, texture_data[stack_depth - 1],
+ texture_data[stack_depth]);
+ }
+ }
+
+ /* We should have just 1 sample on the stack now. */
+ assert(stack_depth == 1);
+
+ texture_data[0] = nir_fmul(b, texture_data[0],
+ nir_imm_float(b, 1.0 / tex_samples));
+
+ nir_store_var(b, color, texture_data[0], 0xf);
+
+ if (outer_if)
+ b->cursor = nir_after_cf_node(&outer_if->cf_node);
+
+ return nir_load_var(b, color);
+}
+
/**
* Generator for WM programs used in BLORP blits.
*
* irrelevant, because we are going to fetch all samples.
*/
if (key->blend && !key->blit_scaled) {
- goto fail;
+ if (brw->gen == 6) {
+ /* Because gen6 only supports 4x interleved MSAA, we can do all the
+ * blending we need with a single linear-interpolated texture lookup
+ * at the center of the sample. The texture coordinates to be odd
+ * integers so that they correspond to the center of a 2x2 block
+ * representing the four samples that maxe up a pixel. So we need
+ * to multiply our X and Y coordinates each by 2 and then add 1.
+ */
+ src_pos = nir_ishl(&b, src_pos, nir_imm_int(&b, 1));
+ src_pos = nir_iadd(&b, src_pos, nir_imm_int(&b, 1));
+ src_pos = nir_i2f(&b, nir_channels(&b, src_pos, 0x3));
+ color = blorp_nir_tex(&b, src_pos, key->texture_data_type);
+ } else {
+ /* Gen7+ hardware doesn't automaticaly blend. */
+ color = blorp_nir_manual_blend_average(&b, src_pos, key->src_samples,
+ key->src_layout,
+ key->texture_data_type);
+ }
} else if (key->blend && key->blit_scaled) {
goto fail;
} else {
-/**
- * Count the number of trailing 1 bits in the given value. For example:
- *
- * count_trailing_one_bits(0) == 0
- * count_trailing_one_bits(7) == 3
- * count_trailing_one_bits(11) == 2
- */
-static inline int count_trailing_one_bits(unsigned value)
-{
-#ifdef HAVE___BUILTIN_CTZ
- return __builtin_ctz(~value);
-#else
- return _mesa_bitcount(value & ~(value + 1));
-#endif
-}
-
-
void
brw_blorp_blit_program::manual_blend_average(unsigned num_samples)
{
projects / mesa.git / commitdiff