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Near/far clipping
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This still doesn't handle large triangles spanning both planes
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@Daft-Freak
Daft-Freak committed Oct 8, 2024
1 parent 4d45198 commit 1d4fdb4
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Showing 2 changed files with 190 additions and 16 deletions.
205 changes: 189 additions & 16 deletions lib/render-3d.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -143,40 +143,119 @@ void Render3D::draw(int count, const uint8_t *ptr)
for(int i = 0; i < count; i += stride)
{
// vertex limit reached
if(trans + 3 >= transformed_vertices + std::size(transformed_vertices))
// check two triangles for clipping pessimism
if(trans + stride + 3 >= transformed_vertices + std::size(transformed_vertices))
break;

// calculate final positions
for(int j = 0; j < 3; j++)
{
position_shader(ptr + (i + j) * vertex_stride, trans + j, *this);
transform_vertex(trans[j]);


// test against near/far planes
int far_out = 0, near_out = 0;

for(int i = 0; i < 3; i++)
{
if(trans[i].z > trans[i].w)
far_out += 1 << i;
else if(trans[i].z < -trans[i].w)
near_out += 1 << i;
}

// cull back faces and empty
if(cull_triangle(trans))
// crosses both planes, that's one big triangle...
if(near_out && far_out)
continue;

// far plane
// TODO: clip
if(trans[0].z > 1 || trans[1].z > 1 || trans[2].z > 1)
// entirely outside
if(near_out == 7 || far_out == 7)
continue;

Fixed32<20> clipped_factors[2 * 3 * 3];
bool add_triangle = false;

// far plane
if(far_out)
add_triangle = clip_triangle(trans, 1, far_out, clipped_factors);
// near plane
// TODO: clip
if(trans[0].z < -1 || trans[1].z < -1 || trans[2].z < -1)
continue;
else if(near_out)
add_triangle = clip_triangle(trans, -1, near_out, clipped_factors);

// calculate the rest of the attributes
for(int j = 0; j < 3; j++) {
// also convert z to uint16
trans[j].z = (trans[j].z + 1) * Fixed32<>(32767.5f);
bool clipped = near_out || far_out;

// calculate the rest of the attributes
for(int j = 0; j < 3; j++)
vertex_shader(ptr + (i + j) * vertex_stride, trans + j, *this);

// apply clipping to attributes now that we have them
if(clipped)
{
VertexOutData temp[3];
// blend ALL the attributes
for(int j = 0; j < 3; j++)
{
temp[j].x = trans[0].x * clipped_factors[j * 3 + 0] + trans[1].x * clipped_factors[j * 3 + 1] + trans[2].x * clipped_factors[j * 3 + 2];
temp[j].y = trans[0].y * clipped_factors[j * 3 + 0] + trans[1].y * clipped_factors[j * 3 + 1] + trans[2].y * clipped_factors[j * 3 + 2];
temp[j].z = trans[0].z * clipped_factors[j * 3 + 0] + trans[1].z * clipped_factors[j * 3 + 1] + trans[2].z * clipped_factors[j * 3 + 2];
temp[j].w = trans[0].w * clipped_factors[j * 3 + 0] + trans[1].w * clipped_factors[j * 3 + 1] + trans[2].w * clipped_factors[j * 3 + 2];

temp[j].r = uint8_t(Fixed32<>(trans[0].r) * clipped_factors[j * 3 + 0] + Fixed32<>(trans[1].r) * clipped_factors[j * 3 + 1] + Fixed32<>(trans[2].r) * clipped_factors[j * 3 + 2]);
temp[j].g = uint8_t(Fixed32<>(trans[0].g) * clipped_factors[j * 3 + 0] + Fixed32<>(trans[1].g) * clipped_factors[j * 3 + 1] + Fixed32<>(trans[2].g) * clipped_factors[j * 3 + 2]);
temp[j].b = uint8_t(Fixed32<>(trans[0].b) * clipped_factors[j * 3 + 0] + Fixed32<>(trans[1].b) * clipped_factors[j * 3 + 1] + Fixed32<>(trans[2].b) * clipped_factors[j * 3 + 2]);

temp[j].tex_index = trans[0].tex_index; // tex index can't be blended

temp[j].u = Fixed16<12>(clipped_factors[j * 3 + 0] * trans[0].u + clipped_factors[j * 3 + 1] * trans[1].u + clipped_factors[j * 3 + 2] * trans[2].u);
temp[j].v = Fixed16<12>(clipped_factors[j * 3 + 0] * trans[0].v + clipped_factors[j * 3 + 1] * trans[1].v + clipped_factors[j * 3 + 2] * trans[2].v);
}

// second tri
if(add_triangle)
{
auto trans2 = trans + stride;
auto factors = clipped_factors + 3 * 3;
for(int j = 0; j < 3; j++)
{
trans2[j].x = trans[0].x * factors[j * 3 + 0] + trans[1].x * factors[j * 3 + 1] + trans[2].x * factors[j * 3 + 2];
trans2[j].y = trans[0].y * factors[j * 3 + 0] + trans[1].y * factors[j * 3 + 1] + trans[2].y * factors[j * 3 + 2];
trans2[j].z = trans[0].z * factors[j * 3 + 0] + trans[1].z * factors[j * 3 + 1] + trans[2].z * factors[j * 3 + 2];
trans2[j].w = trans[0].w * factors[j * 3 + 0] + trans[1].w * factors[j * 3 + 1] + trans[2].w * factors[j * 3 + 2];

trans2[j].r = uint8_t(Fixed32<>(trans[0].r) * factors[j * 3 + 0] + Fixed32<>(trans[1].r) * factors[j * 3 + 1] + Fixed32<>(trans[2].r) * factors[j * 3 + 2]);
trans2[j].g = uint8_t(Fixed32<>(trans[0].g) * factors[j * 3 + 0] + Fixed32<>(trans[1].g) * factors[j * 3 + 1] + Fixed32<>(trans[2].g) * factors[j * 3 + 2]);
trans2[j].b = uint8_t(Fixed32<>(trans[0].b) * factors[j * 3 + 0] + Fixed32<>(trans[1].b) * factors[j * 3 + 1] + Fixed32<>(trans[2].b) * factors[j * 3 + 2]);

trans2[j].tex_index = trans[0].tex_index; // tex index can't be blended

trans2[j].u = Fixed16<12>(factors[j * 3 + 0] * trans[0].u + factors[j * 3 + 1] * trans[1].u + factors[j * 3 + 2] * trans[2].u);
trans2[j].v = Fixed16<12>(factors[j * 3 + 0] * trans[0].v + factors[j * 3 + 1] * trans[1].v + factors[j * 3 + 2] * trans[2].v);

transform_vertex(trans2[j]);
trans2[j].z = (trans2[j].z + 1) * Fixed32<>(32767.5f); //
}

// cull new triangle
add_triangle = !cull_triangle(trans2);
}

memcpy(trans, temp, sizeof(VertexOutData) * 3);
}

// TODO: clipping
// w divide and viewport transform
for(int j = 0; j < 3; j++)
{
transform_vertex(trans[j]);
trans[j].z = (trans[j].z + 1) * Fixed32<>(32767.5f); // move back to transform_vertex
}

// cull back faces and empty
if(cull_triangle(trans))
continue;

trans += stride;

if(add_triangle)
trans += stride;
}

#if PICO_MULTICORE
Expand Down Expand Up @@ -441,6 +520,100 @@ bool Render3D::cull_triangle(VertexOutData *verts)
return false;
}

bool Render3D::clip_triangle(VertexOutData *verts, Fixed32<> bound, int verts_outside, Fixed32<20> out_factors[2 * 3 * 3])
{
// there's one vertex on one side and two on the other
// just need to figure out which is which... and which way around it is
VertexOutData *a, *b, *c;

bool one_outside = !(verts_outside & (verts_outside - 1));
int a_index;

if(one_outside)
{
// one vert outside, two inside (result is two triangles)
a_index = verts_outside / 2; // 1,2,4 -> 0,1,2
}
else
{
// two verts outside, one inside (result is one triangle)
auto inside = ~verts_outside & 7;
a_index = inside / 2; // 1,2,4 -> 0,1,2
}

a = verts + a_index;
b = verts + (a_index + 1) % 3;
c = verts + (a_index + 2) % 3;

// we've got our vertices, now intersect the edges (a-b and a-c)
// (bound is +/-1 used to flip for far/near plane)
Fixed32<20> bf, cf;

bf = Fixed32<20>(a->w - a->z * bound) / Fixed32<20>((a->w - a->z * bound) - (b->w - b->z * bound));
cf = Fixed32<20>(a->w - a->z * bound) / Fixed32<20>((a->w - a->z * bound) - (c->w - c->z * bound));

int b_index = b - verts;
int c_index = c - verts;

// and setup the factors for the new triangles
// (can't build them yet, we don't have the attributes)
if(one_outside)
{
// A = B * bf + A * (1 - bf)
out_factors[a_index * 3 + a_index] = Fixed32<20>(1) - bf;
out_factors[a_index * 3 + b_index] = bf;
out_factors[a_index * 3 + c_index] = 0;

// B = B
out_factors[b_index * 3 + a_index] = 0;
out_factors[b_index * 3 + b_index] = 1;
out_factors[b_index * 3 + c_index] = 0;

// C = C
out_factors[c_index * 3 + a_index] = 0;
out_factors[c_index * 3 + b_index] = 0;
out_factors[c_index * 3 + c_index] = 1;

// second triangle

// A = B * bf + A * (1 - bf)
out_factors[(a_index + 3) * 3 + a_index] = Fixed32<20>(1) - bf;
out_factors[(a_index + 3) * 3 + b_index] = bf;
out_factors[(a_index + 3) * 3 + c_index] = 0;

// B = C
out_factors[(b_index + 3) * 3 + a_index] = 0;
out_factors[(b_index + 3) * 3 + b_index] = 0;
out_factors[(b_index + 3) * 3 + c_index] = 1;

// C = C * cf + A * (1 - cf)
out_factors[(c_index + 3) * 3 + a_index] = Fixed32<20>(1) - cf;
out_factors[(c_index + 3) * 3 + b_index] = 0;
out_factors[(c_index + 3) * 3 + c_index] = cf;
return true;
}
else
{
// A = A
out_factors[a_index * 3 + a_index] = 1;
out_factors[a_index * 3 + b_index] = 0;
out_factors[a_index * 3 + c_index] = 0;

// B = B * bf + A * (1 - bf)
out_factors[b_index * 3 + a_index] = Fixed32<20>(1) - bf;
out_factors[b_index * 3 + b_index] = bf;
out_factors[b_index * 3 + c_index] = 0;

// C = C * cf + A * (1 - cf)
out_factors[c_index * 3 + a_index] = Fixed32<20>(1) - cf;
out_factors[c_index * 3 + b_index] = 0;
out_factors[c_index * 3 + c_index] = cf;

// no second triangle
return false;
}
}

void blit_fast_code(Render3D::fill_triangle)(VertexOutData *data, blit::Point tile_pos)
{
struct IntVec3
Expand Down
1 change: 1 addition & 0 deletions lib/render-3d.hpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -48,6 +48,7 @@ class Render3D
void transform_vertex(VertexOutData &pos);

bool cull_triangle(VertexOutData *verts);
bool clip_triangle(VertexOutData *verts, Fixed32<> bound, int verts_outside, Fixed32<20> out_factors[2 * 3 * 3]);

void fill_triangle(VertexOutData *data, blit::Point tile_pos);

Expand Down

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