+/*
+ * Copyright 2019 Advanced Micro Devices, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sub license, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDERS, AUTHORS AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM,
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+ * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+ * USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial portions
+ * of the Software.
+ *
+ */
+
+#include "ac_llvm_cull.h"
+#include <llvm-c/Core.h>
+
+struct ac_position_w_info {
+ /* If a primitive intersects the W=0 plane, it causes a reflection
+ * of the determinant used for face culling. Every vertex behind
+ * the W=0 plane negates the determinant, so having 2 vertices behind
+ * the plane has no effect. This is i1 true if the determinant should be
+ * negated.
+ */
+ LLVMValueRef w_reflection;
+
+ /* If we simplify the "-w <= p <= w" view culling equation, we get
+ * "-w <= w", which can't be satisfied when w is negative.
+ * In perspective projection, a negative W means that the primitive
+ * is behind the viewer, but the equation is independent of the type
+ * of projection.
+ *
+ * w_accepted is false when all W are negative and therefore
+ * the primitive is invisible.
+ */
+ LLVMValueRef w_accepted;
+
+ LLVMValueRef all_w_positive;
+ LLVMValueRef any_w_negative;
+};
+
+static void ac_analyze_position_w(struct ac_llvm_context *ctx,
+ LLVMValueRef pos[3][4],
+ struct ac_position_w_info *w)
+{
+ LLVMBuilderRef builder = ctx->builder;
+ LLVMValueRef all_w_negative = ctx->i1true;
+
+ w->w_reflection = ctx->i1false;
+ w->any_w_negative = ctx->i1false;
+
+ for (unsigned i = 0; i < 3; i++) {
+ LLVMValueRef neg_w;
+
+ neg_w = LLVMBuildFCmp(builder, LLVMRealOLT, pos[i][3], ctx->f32_0, "");
+ /* If neg_w is true, negate w_reflection. */
+ w->w_reflection = LLVMBuildXor(builder, w->w_reflection, neg_w, "");
+ w->any_w_negative = LLVMBuildOr(builder, w->any_w_negative, neg_w, "");
+ all_w_negative = LLVMBuildAnd(builder, all_w_negative, neg_w, "");
+ }
+ w->all_w_positive = LLVMBuildNot(builder, w->any_w_negative, "");
+ w->w_accepted = LLVMBuildNot(builder, all_w_negative, "");
+}
+
+/* Perform front/back face culling and return true if the primitive is accepted. */
+static LLVMValueRef ac_cull_face(struct ac_llvm_context *ctx,
+ LLVMValueRef pos[3][4],
+ struct ac_position_w_info *w,
+ bool cull_front,
+ bool cull_back,
+ bool cull_zero_area)
+{
+ LLVMBuilderRef builder = ctx->builder;
+
+ if (cull_front && cull_back)
+ return ctx->i1false;
+
+ if (!cull_front && !cull_back && !cull_zero_area)
+ return ctx->i1true;
+
+ /* Front/back face culling. Also if the determinant == 0, the triangle
+ * area is 0.
+ */
+ LLVMValueRef det_t0 = LLVMBuildFSub(builder, pos[2][0], pos[0][0], "");
+ LLVMValueRef det_t1 = LLVMBuildFSub(builder, pos[1][1], pos[0][1], "");
+ LLVMValueRef det_t2 = LLVMBuildFSub(builder, pos[0][0], pos[1][0], "");
+ LLVMValueRef det_t3 = LLVMBuildFSub(builder, pos[0][1], pos[2][1], "");
+ LLVMValueRef det_p0 = LLVMBuildFMul(builder, det_t0, det_t1, "");
+ LLVMValueRef det_p1 = LLVMBuildFMul(builder, det_t2, det_t3, "");
+ LLVMValueRef det = LLVMBuildFSub(builder, det_p0, det_p1, "");
+
+ /* Negative W negates the determinant. */
+ det = LLVMBuildSelect(builder, w->w_reflection,
+ LLVMBuildFNeg(builder, det, ""),
+ det, "");
+
+ LLVMValueRef accepted = NULL;
+ if (cull_front) {
+ LLVMRealPredicate cond = cull_zero_area ? LLVMRealOGT : LLVMRealOGE;
+ accepted = LLVMBuildFCmp(builder, cond, det, ctx->f32_0, "");
+ } else if (cull_back) {
+ LLVMRealPredicate cond = cull_zero_area ? LLVMRealOLT : LLVMRealOLE;
+ accepted = LLVMBuildFCmp(builder, cond, det, ctx->f32_0, "");
+ } else if (cull_zero_area) {
+ accepted = LLVMBuildFCmp(builder, LLVMRealONE, det, ctx->f32_0, "");
+ }
+ return accepted;
+}
+
+/* Perform view culling and small primitive elimination and return true
+ * if the primitive is accepted and initially_accepted == true. */
+static LLVMValueRef cull_bbox(struct ac_llvm_context *ctx,
+ LLVMValueRef pos[3][4],
+ LLVMValueRef initially_accepted,
+ struct ac_position_w_info *w,
+ LLVMValueRef vp_scale[2],
+ LLVMValueRef vp_translate[2],
+ LLVMValueRef small_prim_precision,
+ bool cull_view_xy,
+ bool cull_view_near_z,
+ bool cull_view_far_z,
+ bool cull_small_prims,
+ bool use_halfz_clip_space)
+{
+ LLVMBuilderRef builder = ctx->builder;
+
+ if (!cull_view_xy && !cull_view_near_z && !cull_view_far_z && !cull_small_prims)
+ return ctx->i1true;
+
+ /* Skip the culling if the primitive has already been rejected or
+ * if any W is negative. The bounding box culling doesn't work when
+ * W is negative.
+ */
+ LLVMValueRef cond = LLVMBuildAnd(builder, initially_accepted,
+ w->all_w_positive, "");
+ LLVMValueRef accepted_var = ac_build_alloca_undef(ctx, ctx->i1, "");
+ LLVMBuildStore(builder, initially_accepted, accepted_var);
+
+ ac_build_ifcc(ctx, cond, 10000000 /* does this matter? */);
+ {
+ LLVMValueRef bbox_min[3], bbox_max[3];
+ LLVMValueRef accepted = initially_accepted;
+
+ /* Compute the primitive bounding box for easy culling. */
+ for (unsigned chan = 0; chan < 3; chan++) {
+ bbox_min[chan] = ac_build_fmin(ctx, pos[0][chan], pos[1][chan]);
+ bbox_min[chan] = ac_build_fmin(ctx, bbox_min[chan], pos[2][chan]);
+
+ bbox_max[chan] = ac_build_fmax(ctx, pos[0][chan], pos[1][chan]);
+ bbox_max[chan] = ac_build_fmax(ctx, bbox_max[chan], pos[2][chan]);
+ }
+
+ /* View culling. */
+ if (cull_view_xy || cull_view_near_z || cull_view_far_z) {
+ for (unsigned chan = 0; chan < 3; chan++) {
+ LLVMValueRef visible;
+
+ if ((cull_view_xy && chan <= 1) ||
+ (cull_view_near_z && chan == 2)) {
+ float t = chan == 2 && use_halfz_clip_space ? 0 : -1;
+ visible = LLVMBuildFCmp(builder, LLVMRealOGE, bbox_max[chan],
+ LLVMConstReal(ctx->f32, t), "");
+ accepted = LLVMBuildAnd(builder, accepted, visible, "");
+ }
+
+ if ((cull_view_xy && chan <= 1) ||
+ (cull_view_far_z && chan == 2)) {
+ visible = LLVMBuildFCmp(builder, LLVMRealOLE, bbox_min[chan],
+ ctx->f32_1, "");
+ accepted = LLVMBuildAnd(builder, accepted, visible, "");
+ }
+ }
+ }
+
+ /* Small primitive elimination. */
+ if (cull_small_prims) {
+ /* Assuming a sample position at (0.5, 0.5), if we round
+ * the bounding box min/max extents and the results of
+ * the rounding are equal in either the X or Y direction,
+ * the bounding box does not intersect the sample.
+ *
+ * See these GDC slides for pictures:
+ * https://frostbite-wp-prd.s3.amazonaws.com/wp-content/uploads/2016/03/29204330/GDC_2016_Compute.pdf
+ */
+ LLVMValueRef min, max, not_equal[2], visible;
+
+ for (unsigned chan = 0; chan < 2; chan++) {
+ /* Convert the position to screen-space coordinates. */
+ min = ac_build_fmad(ctx, bbox_min[chan],
+ vp_scale[chan], vp_translate[chan]);
+ max = ac_build_fmad(ctx, bbox_max[chan],
+ vp_scale[chan], vp_translate[chan]);
+ /* Scale the bounding box according to the precision of
+ * the rasterizer and the number of MSAA samples. */
+ min = LLVMBuildFSub(builder, min, small_prim_precision, "");
+ max = LLVMBuildFAdd(builder, max, small_prim_precision, "");
+
+ /* Determine if the bbox intersects the sample point.
+ * It also works for MSAA, but vp_scale, vp_translate,
+ * and small_prim_precision are computed differently.
+ */
+ min = ac_build_round(ctx, min);
+ max = ac_build_round(ctx, max);
+ not_equal[chan] = LLVMBuildFCmp(builder, LLVMRealONE, min, max, "");
+ }
+ visible = LLVMBuildAnd(builder, not_equal[0], not_equal[1], "");
+ accepted = LLVMBuildAnd(builder, accepted, visible, "");
+ }
+
+ LLVMBuildStore(builder, accepted, accepted_var);
+ }
+ ac_build_endif(ctx, 10000000);
+
+ return LLVMBuildLoad(builder, accepted_var, "");
+}
+
+/**
+ * Return i1 true if the primitive is accepted (not culled).
+ *
+ * \param pos Vertex positions 3x vec4
+ * \param initially_accepted AND'ed with the result. Some computations can be
+ * skipped if this is false.
+ * \param vp_scale Viewport scale XY.
+ * For MSAA, multiply them by the number of samples.
+ * \param vp_translate Viewport translation XY.
+ * For MSAA, multiply them by the number of samples.
+ * \param small_prim_precision Precision of small primitive culling. This should
+ * be the same as or greater than the precision of
+ * the rasterizer. Set to num_samples / 2^subpixel_bits.
+ * subpixel_bits are defined by the quantization mode.
+ * \param options See ac_cull_options.
+ */
+LLVMValueRef ac_cull_triangle(struct ac_llvm_context *ctx,
+ LLVMValueRef pos[3][4],
+ LLVMValueRef initially_accepted,
+ LLVMValueRef vp_scale[2],
+ LLVMValueRef vp_translate[2],
+ LLVMValueRef small_prim_precision,
+ struct ac_cull_options *options)
+{
+ struct ac_position_w_info w;
+ ac_analyze_position_w(ctx, pos, &w);
+
+ /* W culling. */
+ LLVMValueRef accepted = options->cull_w ? w.w_accepted : ctx->i1true;
+ accepted = LLVMBuildAnd(ctx->builder, accepted, initially_accepted, "");
+
+ /* Face culling. */
+ accepted = LLVMBuildAnd(ctx->builder, accepted,
+ ac_cull_face(ctx, pos, &w,
+ options->cull_front,
+ options->cull_back,
+ options->cull_zero_area), "");
+
+ /* View culling and small primitive elimination. */
+ accepted = cull_bbox(ctx, pos, accepted, &w, vp_scale, vp_translate,
+ small_prim_precision,
+ options->cull_view_xy,
+ options->cull_view_near_z,
+ options->cull_view_far_z,
+ options->cull_small_prims,
+ options->use_halfz_clip_space);
+ return accepted;
+}
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