360 lines
16 KiB
C
360 lines
16 KiB
C
/*
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* Copyright 2019 Advanced Micro Devices, Inc.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sub license, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
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* THE COPYRIGHT HOLDERS, AUTHORS AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM,
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* DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
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* OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
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* USE OR OTHER DEALINGS IN THE SOFTWARE.
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*
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* The above copyright notice and this permission notice (including the
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* next paragraph) shall be included in all copies or substantial portions
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* of the Software.
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*
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*/
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#include "ac_llvm_cull.h"
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#include <llvm-c/Core.h>
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struct ac_position_w_info {
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/* If a primitive intersects the W=0 plane, it causes a reflection
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* of the determinant used for face culling. Every vertex behind
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* the W=0 plane negates the determinant, so having 2 vertices behind
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* the plane has no effect. This is i1 true if the determinant should be
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* negated.
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*/
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LLVMValueRef w_reflection;
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/* If we simplify the "-w <= p <= w" view culling equation, we get
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* "-w <= w", which can't be satisfied when w is negative.
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* In perspective projection, a negative W means that the primitive
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* is behind the viewer, but the equation is independent of the type
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* of projection.
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*
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* w_accepted is false when all W are negative and therefore
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* the primitive is invisible.
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*/
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LLVMValueRef w_accepted;
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/* The bounding box culling doesn't work and should be skipped when this is true. */
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LLVMValueRef any_w_negative;
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};
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static void ac_analyze_position_w(struct ac_llvm_context *ctx, LLVMValueRef pos[3][4],
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struct ac_position_w_info *w, unsigned num_vertices)
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{
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LLVMBuilderRef builder = ctx->builder;
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LLVMValueRef all_w_negative = ctx->i1true;
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w->w_reflection = ctx->i1false;
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w->any_w_negative = ctx->i1false;
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for (unsigned i = 0; i < num_vertices; i++) {
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LLVMValueRef neg_w;
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neg_w = LLVMBuildFCmp(builder, LLVMRealOLT, pos[i][3], ctx->f32_0, "");
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/* If neg_w is true, negate w_reflection. */
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w->w_reflection = LLVMBuildXor(builder, w->w_reflection, neg_w, "");
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w->any_w_negative = LLVMBuildOr(builder, w->any_w_negative, neg_w, "");
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all_w_negative = LLVMBuildAnd(builder, all_w_negative, neg_w, "");
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}
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w->w_accepted = LLVMBuildNot(builder, all_w_negative, "");
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}
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/* Perform front/back face culling and return true if the primitive is accepted. */
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static LLVMValueRef ac_cull_face(struct ac_llvm_context *ctx, LLVMValueRef pos[3][4],
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struct ac_position_w_info *w, bool cull_front, bool cull_back,
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bool cull_zero_area)
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{
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LLVMBuilderRef builder = ctx->builder;
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if (cull_front && cull_back)
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return ctx->i1false;
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if (!cull_front && !cull_back && !cull_zero_area)
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return ctx->i1true;
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/* Front/back face culling. Also if the determinant == 0, the triangle
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* area is 0.
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*/
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LLVMValueRef det_t0 = LLVMBuildFSub(builder, pos[2][0], pos[0][0], "");
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LLVMValueRef det_t1 = LLVMBuildFSub(builder, pos[1][1], pos[0][1], "");
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LLVMValueRef det_t2 = LLVMBuildFSub(builder, pos[0][0], pos[1][0], "");
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LLVMValueRef det_t3 = LLVMBuildFSub(builder, pos[0][1], pos[2][1], "");
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/* t0 * t1 - t2 * t3 = t2 * -t3 + t0 * t1 = fma(t2, -t3, t0 * t1) */
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LLVMValueRef det = ac_build_fmad(ctx, det_t2, LLVMBuildFNeg(builder, det_t3, ""),
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LLVMBuildFMul(builder, det_t0, det_t1, ""));
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/* Negative W negates the determinant. */
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det = LLVMBuildSelect(builder, w->w_reflection, LLVMBuildFNeg(builder, det, ""), det, "");
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LLVMValueRef accepted = NULL;
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if (cull_front) {
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LLVMRealPredicate cond = cull_zero_area ? LLVMRealOGT : LLVMRealOGE;
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accepted = LLVMBuildFCmp(builder, cond, det, ctx->f32_0, "");
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} else if (cull_back) {
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LLVMRealPredicate cond = cull_zero_area ? LLVMRealOLT : LLVMRealOLE;
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accepted = LLVMBuildFCmp(builder, cond, det, ctx->f32_0, "");
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} else if (cull_zero_area) {
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accepted = LLVMBuildFCmp(builder, LLVMRealONE, det, ctx->f32_0, "");
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}
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if (accepted) {
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/* Don't reject NaN and +/-infinity, these are tricky.
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* Just trust fixed-function HW to handle these cases correctly.
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*/
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accepted = LLVMBuildOr(builder, accepted, ac_build_is_inf_or_nan(ctx, det), "");
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}
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return accepted;
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}
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static void rotate_45degrees(struct ac_llvm_context *ctx, LLVMValueRef v[2])
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{
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/* sin(45) == cos(45) */
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LLVMValueRef sincos45 = LLVMConstReal(ctx->f32, 0.707106781);
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/* x2 = x*cos45 - y*sin45 = x*sincos45 - y*sincos45
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* y2 = x*sin45 + y*cos45 = x*sincos45 + y*sincos45
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*/
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LLVMValueRef first = LLVMBuildFMul(ctx->builder, v[0], sincos45, "");
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/* Doing 2x ffma while duplicating the multiplication is 33% faster than fmul+fadd+fadd. */
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LLVMValueRef result[2] = {
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ac_build_fmad(ctx, LLVMBuildFNeg(ctx->builder, v[1], ""), sincos45, first),
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ac_build_fmad(ctx, v[1], sincos45, first),
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};
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memcpy(v, result, sizeof(result));
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}
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/* Perform view culling and small primitive elimination and return true
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* if the primitive is accepted and initially_accepted == true. */
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static void cull_bbox(struct ac_llvm_context *ctx, LLVMValueRef pos[3][4],
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LLVMValueRef initially_accepted, struct ac_position_w_info *w,
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LLVMValueRef vp_scale[2], LLVMValueRef vp_translate[2],
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LLVMValueRef small_prim_precision,
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LLVMValueRef clip_half_line_width[2],
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struct ac_cull_options *options,
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ac_cull_accept_func accept_func, void *userdata)
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{
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LLVMBuilderRef builder = ctx->builder;
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if (!options->cull_view_xy && !options->cull_view_near_z && !options->cull_view_far_z &&
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!options->cull_small_prims) {
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if (accept_func)
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accept_func(ctx, initially_accepted, userdata);
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return;
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}
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ac_build_ifcc(ctx, initially_accepted, 10000000);
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{
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LLVMValueRef bbox_min[3], bbox_max[3];
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LLVMValueRef accepted = ctx->i1true;
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/* Compute the primitive bounding box for easy culling. */
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for (unsigned chan = 0; chan < (options->cull_view_near_z ||
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options->cull_view_far_z ? 3 : 2); chan++) {
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assert(options->num_vertices >= 2);
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bbox_min[chan] = ac_build_fmin(ctx, pos[0][chan], pos[1][chan]);
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bbox_max[chan] = ac_build_fmax(ctx, pos[0][chan], pos[1][chan]);
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if (options->num_vertices == 3) {
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bbox_min[chan] = ac_build_fmin(ctx, bbox_min[chan], pos[2][chan]);
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bbox_max[chan] = ac_build_fmax(ctx, bbox_max[chan], pos[2][chan]);
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}
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if (clip_half_line_width[chan]) {
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bbox_min[chan] = LLVMBuildFSub(builder, bbox_min[chan], clip_half_line_width[chan], "");
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bbox_max[chan] = LLVMBuildFAdd(builder, bbox_max[chan], clip_half_line_width[chan], "");
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}
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}
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/* View culling. */
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if (options->cull_view_xy || options->cull_view_near_z || options->cull_view_far_z) {
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for (unsigned chan = 0; chan < 3; chan++) {
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LLVMValueRef visible;
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if ((options->cull_view_xy && chan <= 1) || (options->cull_view_near_z && chan == 2)) {
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float t = chan == 2 && options->use_halfz_clip_space ? 0 : -1;
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visible = LLVMBuildFCmp(builder, LLVMRealOGE, bbox_max[chan],
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LLVMConstReal(ctx->f32, t), "");
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accepted = LLVMBuildAnd(builder, accepted, visible, "");
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}
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if ((options->cull_view_xy && chan <= 1) || (options->cull_view_far_z && chan == 2)) {
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visible = LLVMBuildFCmp(builder, LLVMRealOLE, bbox_min[chan], ctx->f32_1, "");
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accepted = LLVMBuildAnd(builder, accepted, visible, "");
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}
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}
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}
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/* Small primitive culling - triangles. */
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if (options->cull_small_prims && options->num_vertices == 3) {
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/* Assuming a sample position at (0.5, 0.5), if we round
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* the bounding box min/max extents and the results of
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* the rounding are equal in either the X or Y direction,
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* the bounding box does not intersect the sample.
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*
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* See these GDC slides for pictures:
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* https://frostbite-wp-prd.s3.amazonaws.com/wp-content/uploads/2016/03/29204330/GDC_2016_Compute.pdf
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*/
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LLVMValueRef min, max, not_equal[2], visible;
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for (unsigned chan = 0; chan < 2; chan++) {
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/* Convert the position to screen-space coordinates. */
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min = ac_build_fmad(ctx, bbox_min[chan], vp_scale[chan], vp_translate[chan]);
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max = ac_build_fmad(ctx, bbox_max[chan], vp_scale[chan], vp_translate[chan]);
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/* Scale the bounding box according to the precision of
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* the rasterizer and the number of MSAA samples. */
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min = LLVMBuildFSub(builder, min, small_prim_precision, "");
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max = LLVMBuildFAdd(builder, max, small_prim_precision, "");
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/* Determine if the bbox intersects the sample point.
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* It also works for MSAA, but vp_scale, vp_translate,
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* and small_prim_precision are computed differently.
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*/
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min = ac_build_round(ctx, min);
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max = ac_build_round(ctx, max);
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not_equal[chan] = LLVMBuildFCmp(builder, LLVMRealONE, min, max, "");
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}
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visible = LLVMBuildAnd(builder, not_equal[0], not_equal[1], "");
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accepted = LLVMBuildAnd(builder, accepted, visible, "");
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}
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/* Small primitive culling - lines. */
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if (options->cull_small_prims && options->num_vertices == 2) {
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/* This only works with lines without perpendicular end caps (lines with perpendicular
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* end caps are rasterized as quads and thus can't be culled as small prims in 99% of
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* cases because line_width >= 1).
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*
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* This takes advantage of the diamont exit rule, which says that every pixel
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* has a diamond inside it touching the pixel boundary and only if a line exits
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* the diamond, that pixel is filled. If a line enters the diamond or stays
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* outside the diamond, the pixel isn't filled.
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*
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* This algorithm is a little simpler than that. The space outside all diamonds also
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* has the same diamond shape, which we'll call corner diamonds.
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*
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* The idea is to cull all lines that are entirely inside a diamond, including
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* corner diamonds. If a line is entirely inside a diamond, it can be culled because
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* it doesn't exit it. If a line is entirely inside a corner diamond, it can be culled
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* because it doesn't enter any diamond and thus can't exit any diamond.
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*
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* The viewport is rotated by 45 degress to turn diamonds into squares, and a bounding
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* box test is used to determine whether a line is entirely inside any square (diamond).
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*
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* The line width doesn't matter. Wide lines only duplicate filled pixels in either X or
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* Y direction from the filled pixels. MSAA also doesn't matter. MSAA should ideally use
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* perpendicular end caps that enable quad rasterization for lines. Thus, this should
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* always use non-MSAA viewport transformation and non-MSAA small prim precision.
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*
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* A good test is piglit/lineloop because it draws 10k subpixel lines in a circle.
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* It should contain no holes if this matches hw behavior.
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*/
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LLVMValueRef v0[2], v1[2];
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/* Get vertex positions in pixels. */
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for (unsigned chan = 0; chan < 2; chan++) {
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v0[chan] = ac_build_fmad(ctx, pos[0][chan], vp_scale[chan], vp_translate[chan]);
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v1[chan] = ac_build_fmad(ctx, pos[1][chan], vp_scale[chan], vp_translate[chan]);
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}
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/* Rotate the viewport by 45 degress, so that diamonds become squares. */
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rotate_45degrees(ctx, v0);
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rotate_45degrees(ctx, v1);
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LLVMValueRef not_equal[2];
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for (unsigned chan = 0; chan < 2; chan++) {
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/* The width of each square is sqrt(0.5), so scale it to 1 because we want
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* round() to give us the position of the closest center of a square (diamond).
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*/
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v0[chan] = LLVMBuildFMul(builder, v0[chan], LLVMConstReal(ctx->f32, 1.414213562), "");
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v1[chan] = LLVMBuildFMul(builder, v1[chan], LLVMConstReal(ctx->f32, 1.414213562), "");
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/* Compute the bounding box around both vertices. We do this because we must
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* enlarge the line area by the precision of the rasterizer.
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*/
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LLVMValueRef min = ac_build_fmin(ctx, v0[chan], v1[chan]);
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LLVMValueRef max = ac_build_fmax(ctx, v0[chan], v1[chan]);
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/* Enlarge the bounding box by the precision of the rasterizer. */
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min = LLVMBuildFSub(builder, min, small_prim_precision, "");
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max = LLVMBuildFAdd(builder, max, small_prim_precision, "");
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/* Round the bounding box corners. If both rounded corners are equal,
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* the bounding box is entirely inside a square (diamond).
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*/
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min = ac_build_round(ctx, min);
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max = ac_build_round(ctx, max);
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not_equal[chan] = LLVMBuildFCmp(builder, LLVMRealONE, min, max, "");
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}
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accepted = LLVMBuildAnd(builder, accepted,
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LLVMBuildOr(builder, not_equal[0], not_equal[1], ""), "");
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}
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/* Disregard the bounding box culling if any W is negative because the code
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* doesn't work with that.
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*/
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accepted = LLVMBuildOr(builder, accepted, w->any_w_negative, "");
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if (accept_func)
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accept_func(ctx, accepted, userdata);
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}
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ac_build_endif(ctx, 10000000);
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}
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/**
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* Return i1 true if the primitive is accepted (not culled).
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*
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* \param pos Vertex positions 3x vec4
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* \param initially_accepted AND'ed with the result. Some computations can be
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* skipped if this is false.
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* \param vp_scale Viewport scale XY.
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* For MSAA, multiply them by the number of samples.
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* \param vp_translate Viewport translation XY.
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* For MSAA, multiply them by the number of samples.
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* \param small_prim_precision Precision of small primitive culling. This should
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* be the same as or greater than the precision of
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* the rasterizer. Set to num_samples / 2^subpixel_bits.
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* subpixel_bits are defined by the quantization mode.
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* \param options See ac_cull_options.
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* \param accept_func Callback invoked in the inner-most branch where the primitive is accepted.
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*/
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void ac_cull_primitive(struct ac_llvm_context *ctx, LLVMValueRef pos[3][4],
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LLVMValueRef initially_accepted, LLVMValueRef vp_scale[2],
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LLVMValueRef vp_translate[2], LLVMValueRef small_prim_precision,
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LLVMValueRef clip_half_line_width[2], struct ac_cull_options *options,
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ac_cull_accept_func accept_func, void *userdata)
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{
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struct ac_position_w_info w;
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ac_analyze_position_w(ctx, pos, &w, options->num_vertices);
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/* W culling. */
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LLVMValueRef accepted = options->cull_w ? w.w_accepted : ctx->i1true;
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accepted = LLVMBuildAnd(ctx->builder, accepted, initially_accepted, "");
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/* Face culling. */
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accepted = LLVMBuildAnd(
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ctx->builder, accepted,
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ac_cull_face(ctx, pos, &w, options->cull_front, options->cull_back, options->cull_zero_area),
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"");
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/* View culling and small primitive elimination. */
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cull_bbox(ctx, pos, accepted, &w, vp_scale, vp_translate, small_prim_precision,
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clip_half_line_width, options, accept_func, userdata);
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}
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