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zink: fix line-smooth interpolation

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Extending the lines by half a pixel in each direction without doing
anything about the varyings makes the varyings interpolate over a
distance than intended. While this can be negligeble for long lines,
it can lead to big error for short lines.

Let's instead add extra geometry for each of the line-caps, so we can
make sure the varyings stay constant for the whole cap, and interpolate
over the intended distance instead.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19847>
This commit is contained in:
Erik Faye-Lund 2022-12-05 16:16:43 +01:00 • committed by Marge Bot
parent 80285db9ef
commit c6cc1dc37c
1 changed files with 15 additions and 7 deletions
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22
src/gallium/drivers/zink/zink_compiler.c
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@ -637,23 +637,31 @@ lower_line_smooth_gs_emit_vertex(nir_builder *b,
tangent = nir_pad_vector_imm_int(b, tangent, 0, 4);
dir = nir_fmul_imm(b, nir_fmul(b, dir, vp_scale_rcp), 0.5);
nir_ssa_def *line_offets[4] = {
nir_ssa_def *line_offets[8] = {
nir_fadd(b, tangent, nir_fneg(b, dir)),
nir_fadd(b, nir_fneg(b, tangent), nir_fneg(b, dir)),
tangent,
nir_fneg(b, tangent),
tangent,
nir_fneg(b, tangent),
nir_fadd(b, tangent, dir),
nir_fadd(b, nir_fneg(b, tangent), dir),
};
nir_ssa_def *line_coord =
nir_vec4(b, half_width, half_width, half_length, half_length);
nir_ssa_def *line_coords[4] = {
nir_ssa_def *line_coords[8] = {
nir_fmul(b, line_coord, nir_imm_vec4(b, -1, 1, -1, 1)),
nir_fmul(b, line_coord, nir_imm_vec4(b, 1, 1, -1, 1)),
nir_fmul(b, line_coord, nir_imm_vec4(b, -1, 1, 0, 1)),
nir_fmul(b, line_coord, nir_imm_vec4(b, 1, 1, 0, 1)),
nir_fmul(b, line_coord, nir_imm_vec4(b, -1, 1, 0, 1)),
nir_fmul(b, line_coord, nir_imm_vec4(b, 1, 1, 0, 1)),
nir_fmul(b, line_coord, nir_imm_vec4(b, -1, 1, 1, 1)),
nir_fmul(b, line_coord, nir_imm_vec4(b, 1, 1, 1, 1)),
};
/* emit first two vertices */
for (int i = 0; i < 2; ++i) {
/* emit first end-cap, and start line */
for (int i = 0; i < 4; ++i) {
nir_foreach_variable_with_modes(var, b->shader, nir_var_shader_out) {
gl_varying_slot location = var->data.location;
if (state->prev_varyings[location])
@ -666,8 +674,8 @@ lower_line_smooth_gs_emit_vertex(nir_builder *b,
nir_emit_vertex(b);
}
/* emit last two vertices */
for (int i = 2; i < 4; ++i) {
/* finish line and emit last end-cap */
for (int i = 4; i < 8; ++i) {
nir_foreach_variable_with_modes(var, b->shader, nir_var_shader_out) {
gl_varying_slot location = var->data.location;
if (state->varyings[location])
@ -794,7 +802,7 @@ lower_line_smooth_gs(nir_shader *shader)
b.cursor = nir_before_cf_list(&entry->body);
nir_store_var(&b, state.pos_counter, nir_imm_int(&b, 0), 1);
shader->info.gs.vertices_out = 2 * shader->info.gs.vertices_out;
shader->info.gs.vertices_out = 8 * shader->info.gs.vertices_out;
shader->info.gs.output_primitive = SHADER_PRIM_TRIANGLE_STRIP;
return nir_shader_instructions_pass(shader, lower_line_smooth_gs_instr,