/* * 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 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; }