/* * 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; /* The bounding box culling doesn't work and should be skipped when this is true. */ 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, unsigned num_vertices) { 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 < num_vertices; 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->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], ""); /* t0 * t1 - t2 * t3 = t2 * -t3 + t0 * t1 = fma(t2, -t3, t0 * t1) */ LLVMValueRef det = ac_build_fmad(ctx, det_t2, LLVMBuildFNeg(builder, det_t3, ""), LLVMBuildFMul(builder, det_t0, det_t1, "")); /* 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, ""); } if (accepted) { /* Don't reject NaN and +/-infinity, these are tricky. * Just trust fixed-function HW to handle these cases correctly. */ accepted = LLVMBuildOr(builder, accepted, ac_build_is_inf_or_nan(ctx, det), ""); } return accepted; } static void rotate_45degrees(struct ac_llvm_context *ctx, LLVMValueRef v[2]) { /* sin(45) == cos(45) */ LLVMValueRef sincos45 = LLVMConstReal(ctx->f32, 0.707106781); /* x2 = x*cos45 - y*sin45 = x*sincos45 - y*sincos45 * y2 = x*sin45 + y*cos45 = x*sincos45 + y*sincos45 */ LLVMValueRef first = LLVMBuildFMul(ctx->builder, v[0], sincos45, ""); /* Doing 2x ffma while duplicating the multiplication is 33% faster than fmul+fadd+fadd. */ LLVMValueRef result[2] = { ac_build_fmad(ctx, LLVMBuildFNeg(ctx->builder, v[1], ""), sincos45, first), ac_build_fmad(ctx, v[1], sincos45, first), }; memcpy(v, result, sizeof(result)); } /* Perform view culling and small primitive elimination and return true * if the primitive is accepted and initially_accepted == true. */ static void 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, LLVMValueRef clip_half_line_width[2], struct ac_cull_options *options, ac_cull_accept_func accept_func, void *userdata) { LLVMBuilderRef builder = ctx->builder; if (!options->cull_view_xy && !options->cull_view_near_z && !options->cull_view_far_z && !options->cull_small_prims) { if (accept_func) accept_func(ctx, initially_accepted, userdata); return; } ac_build_ifcc(ctx, initially_accepted, 10000000); { LLVMValueRef bbox_min[3], bbox_max[3]; LLVMValueRef accepted = ctx->i1true; /* Compute the primitive bounding box for easy culling. */ for (unsigned chan = 0; chan < (options->cull_view_near_z || options->cull_view_far_z ? 3 : 2); chan++) { assert(options->num_vertices >= 2); bbox_min[chan] = ac_build_fmin(ctx, pos[0][chan], pos[1][chan]); bbox_max[chan] = ac_build_fmax(ctx, pos[0][chan], pos[1][chan]); if (options->num_vertices == 3) { bbox_min[chan] = ac_build_fmin(ctx, bbox_min[chan], pos[2][chan]); bbox_max[chan] = ac_build_fmax(ctx, bbox_max[chan], pos[2][chan]); } if (clip_half_line_width[chan]) { bbox_min[chan] = LLVMBuildFSub(builder, bbox_min[chan], clip_half_line_width[chan], ""); bbox_max[chan] = LLVMBuildFAdd(builder, bbox_max[chan], clip_half_line_width[chan], ""); } } /* View culling. */ if (options->cull_view_xy || options->cull_view_near_z || options->cull_view_far_z) { for (unsigned chan = 0; chan < 3; chan++) { LLVMValueRef visible; if ((options->cull_view_xy && chan <= 1) || (options->cull_view_near_z && chan == 2)) { float t = chan == 2 && options->use_halfz_clip_space ? 0 : -1; visible = LLVMBuildFCmp(builder, LLVMRealOGE, bbox_max[chan], LLVMConstReal(ctx->f32, t), ""); accepted = LLVMBuildAnd(builder, accepted, visible, ""); } if ((options->cull_view_xy && chan <= 1) || (options->cull_view_far_z && chan == 2)) { visible = LLVMBuildFCmp(builder, LLVMRealOLE, bbox_min[chan], ctx->f32_1, ""); accepted = LLVMBuildAnd(builder, accepted, visible, ""); } } } /* Small primitive culling - triangles. */ if (options->cull_small_prims && options->num_vertices == 3) { /* 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, ""); } /* Small primitive culling - lines. */ if (options->cull_small_prims && options->num_vertices == 2) { /* This only works with lines without perpendicular end caps (lines with perpendicular * end caps are rasterized as quads and thus can't be culled as small prims in 99% of * cases because line_width >= 1). * * This takes advantage of the diamont exit rule, which says that every pixel * has a diamond inside it touching the pixel boundary and only if a line exits * the diamond, that pixel is filled. If a line enters the diamond or stays * outside the diamond, the pixel isn't filled. * * This algorithm is a little simpler than that. The space outside all diamonds also * has the same diamond shape, which we'll call corner diamonds. * * The idea is to cull all lines that are entirely inside a diamond, including * corner diamonds. If a line is entirely inside a diamond, it can be culled because * it doesn't exit it. If a line is entirely inside a corner diamond, it can be culled * because it doesn't enter any diamond and thus can't exit any diamond. * * The viewport is rotated by 45 degress to turn diamonds into squares, and a bounding * box test is used to determine whether a line is entirely inside any square (diamond). * * The line width doesn't matter. Wide lines only duplicate filled pixels in either X or * Y direction from the filled pixels. MSAA also doesn't matter. MSAA should ideally use * perpendicular end caps that enable quad rasterization for lines. Thus, this should * always use non-MSAA viewport transformation and non-MSAA small prim precision. * * A good test is piglit/lineloop because it draws 10k subpixel lines in a circle. * It should contain no holes if this matches hw behavior. */ LLVMValueRef v0[2], v1[2]; /* Get vertex positions in pixels. */ for (unsigned chan = 0; chan < 2; chan++) { v0[chan] = ac_build_fmad(ctx, pos[0][chan], vp_scale[chan], vp_translate[chan]); v1[chan] = ac_build_fmad(ctx, pos[1][chan], vp_scale[chan], vp_translate[chan]); } /* Rotate the viewport by 45 degress, so that diamonds become squares. */ rotate_45degrees(ctx, v0); rotate_45degrees(ctx, v1); LLVMValueRef not_equal[2]; for (unsigned chan = 0; chan < 2; chan++) { /* The width of each square is sqrt(0.5), so scale it to 1 because we want * round() to give us the position of the closest center of a square (diamond). */ v0[chan] = LLVMBuildFMul(builder, v0[chan], LLVMConstReal(ctx->f32, 1.414213562), ""); v1[chan] = LLVMBuildFMul(builder, v1[chan], LLVMConstReal(ctx->f32, 1.414213562), ""); /* Compute the bounding box around both vertices. We do this because we must * enlarge the line area by the precision of the rasterizer. */ LLVMValueRef min = ac_build_fmin(ctx, v0[chan], v1[chan]); LLVMValueRef max = ac_build_fmax(ctx, v0[chan], v1[chan]); /* Enlarge the bounding box by the precision of the rasterizer. */ min = LLVMBuildFSub(builder, min, small_prim_precision, ""); max = LLVMBuildFAdd(builder, max, small_prim_precision, ""); /* Round the bounding box corners. If both rounded corners are equal, * the bounding box is entirely inside a square (diamond). */ min = ac_build_round(ctx, min); max = ac_build_round(ctx, max); not_equal[chan] = LLVMBuildFCmp(builder, LLVMRealONE, min, max, ""); } accepted = LLVMBuildAnd(builder, accepted, LLVMBuildOr(builder, not_equal[0], not_equal[1], ""), ""); } /* Disregard the bounding box culling if any W is negative because the code * doesn't work with that. */ accepted = LLVMBuildOr(builder, accepted, w->any_w_negative, ""); if (accept_func) accept_func(ctx, accepted, userdata); } ac_build_endif(ctx, 10000000); } /** * 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. * \param accept_func Callback invoked in the inner-most branch where the primitive is accepted. */ void ac_cull_primitive(struct ac_llvm_context *ctx, LLVMValueRef pos[3][4], LLVMValueRef initially_accepted, LLVMValueRef vp_scale[2], LLVMValueRef vp_translate[2], LLVMValueRef small_prim_precision, LLVMValueRef clip_half_line_width[2], struct ac_cull_options *options, ac_cull_accept_func accept_func, void *userdata) { struct ac_position_w_info w; ac_analyze_position_w(ctx, pos, &w, options->num_vertices); /* 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. */ cull_bbox(ctx, pos, accepted, &w, vp_scale, vp_translate, small_prim_precision, clip_half_line_width, options, accept_func, userdata); }