GLdc/GL/clip.c

#include <float.h>
#include <stdio.h>
#include <assert.h>
#include <string.h>

#ifdef _arch_dreamcast
#include <dc/pvr.h>
#else
#define PVR_PACK_COLOR(a, r, g, b) {}
#endif

#include "profiler.h"
#include "private.h"
#include "../containers/aligned_vector.h"


static unsigned char ZCLIP_ENABLED = 1;

unsigned char _glIsClippingEnabled() {
    return ZCLIP_ENABLED;
}

void _glEnableClipping(unsigned char v) {
    ZCLIP_ENABLED = v;
}

void _glClipLineToNearZ(const ClipVertex* v1, const ClipVertex* v2, ClipVertex* vout, float* t) __attribute__((optimize("fast-math")));
void _glClipLineToNearZ(const ClipVertex* v1, const ClipVertex* v2, ClipVertex* vout, float* t) {
    const float NEAR_PLANE = 0.2; // FIXME: this needs to be read from the projection matrix.. somehow

    *t = (NEAR_PLANE - v1->w) / (v2->w - v1->w);

    float vec [] = {v2->xyz[0] - v1->xyz[0], v2->xyz[1] - v1->xyz[1], v2->xyz[2] - v1->xyz[2]};

    vout->xyz[0] = v1->xyz[0] + (vec[0] * (*t));
    vout->xyz[1] = v1->xyz[1] + (vec[1] * (*t));
    vout->xyz[2] = v1->xyz[2] + (vec[2] * (*t));
}

static inline void interpolateFloat(const float v1, const float v2, const float t, float* out) {
    float v = v2 - v1;
    *out = (v * t) + v1;
}

static inline void interpolateVec2(const float* v1, const float* v2, const float t, float* out) {
    /* FIXME: SH4 has an asm instruction for this */
    interpolateFloat(v1[0], v2[0], t, &out[0]);
    interpolateFloat(v1[1], v2[1], t, &out[1]);
}

static inline void interpolateVec3(const float* v1, const float* v2, const float t, float* out) {
    /* FIXME: SH4 has an asm instruction for this */

    interpolateFloat(v1[0], v2[0], t, &out[0]);
    interpolateFloat(v1[1], v2[1], t, &out[1]);
    interpolateFloat(v1[2], v2[2], t, &out[2]);
}

static inline void interpolateVec4(const float* v1, const float* v2, const float t, float* out) {
    /* FIXME: SH4 has an asm instruction for this */
    interpolateFloat(v1[0], v2[0], t, &out[0]);
    interpolateFloat(v1[1], v2[1], t, &out[1]);
    interpolateFloat(v1[2], v2[2], t, &out[2]);
    interpolateFloat(v1[3], v2[3], t, &out[3]);
}

static inline void interpolateColour(const uint8_t* v1, const uint8_t* v2, const float t, uint8_t* out) {
    out[0] = v1[0] + (uint32_t) (((float) (v2[0] - v1[0])) * t);
    out[1] = v1[1] + (uint32_t) (((float) (v2[1] - v1[1])) * t);
    out[2] = v1[2] + (uint32_t) (((float) (v2[2] - v1[2])) * t);
    out[3] = v1[3] + (uint32_t) (((float) (v2[3] - v1[3])) * t);
}

const uint32_t VERTEX_CMD_EOL = 0xf0000000;
const uint32_t VERTEX_CMD = 0xe0000000;

typedef struct {
    ClipVertex vertex[3];
    VertexExtra extra[3];
    uint8_t visible;
} Triangle;

void _glClipTriangle(const Triangle* triangle, const uint8_t visible, SubmissionTarget* target, const uint8_t flatShade) __attribute__((optimize("fast-math")));
void _glClipTriangle(const Triangle* triangle, const uint8_t visible, SubmissionTarget* target, const uint8_t flatShade) {
    uint8_t i, c = 0;

    uint8_t lastVisible = 255;
    ClipVertex* last = NULL;
    VertexExtra* veLast = NULL;

    const ClipVertex* vertices = triangle->vertex;
    const VertexExtra* extras = triangle->extra;

    /* Used when flat shading is enabled */
    uint32_t finalColour = *((uint32_t*) vertices[2].bgra);

    for(i = 0; i < 4; ++i) {
        uint8_t thisIndex = (i == 3) ? 0 : i;

        ClipVertex next;
        VertexExtra veNext;

        next.flags = VERTEX_CMD;

        uint8_t thisVisible = (visible & (1 << (2 - thisIndex))) > 0;
        if(i > 0) {
            uint8_t lastIndex = (i == 3) ? 2 : thisIndex - 1;

            if(lastVisible < 255 && lastVisible != thisVisible) {
                const ClipVertex* v1 = &vertices[lastIndex];
                const ClipVertex* v2 = &vertices[thisIndex];

                const VertexExtra* ve1 = &extras[lastIndex];
                const VertexExtra* ve2 = &extras[thisIndex];

                float t;

                _glClipLineToNearZ(v1, v2, &next, &t);
                interpolateFloat(v1->w, v2->w, t, &next.w);
                interpolateVec2(v1->uv, v2->uv, t, next.uv);

                interpolateVec3(ve1->nxyz, ve2->nxyz, t, veNext.nxyz);
                interpolateVec2(ve1->st, ve2->st, t, veNext.st);

                if(flatShade) {
                    *((uint32_t*) next.bgra) = finalColour;
                } else {
                    interpolateColour(v1->bgra, v2->bgra, t, next.bgra);
                }

                /* Push back the new vertices to the end of both the ClipVertex and VertexExtra lists */
                last = aligned_vector_push_back(&target->output->vector, &next, 1);
                last->flags = VERTEX_CMD;

                veLast = aligned_vector_push_back(target->extras, &veNext, 1);

                ++c;
            }
        }

        if(thisVisible && i != 3) {
            last = aligned_vector_push_back(&target->output->vector, &vertices[thisIndex], 1);
            last->flags = VERTEX_CMD;

            veLast = aligned_vector_push_back(target->extras, &extras[thisIndex], 1);

            ++c;
        }

        lastVisible = thisVisible;
    }

    if(last) {
        if(c == 4) {
            /* Convert to two triangles */
            ClipVertex newVerts[3];
            newVerts[0] = *(last - 3);
            newVerts[1] = *(last - 1);
            newVerts[2] = *(last);

            VertexExtra newExtras[3];
            newExtras[0] = *(veLast - 3);
            newExtras[1] = *(veLast - 1);
            newExtras[2] = *(veLast);

            (last - 1)->flags = VERTEX_CMD_EOL;
            newVerts[0].flags = VERTEX_CMD;
            newVerts[1].flags = VERTEX_CMD;
            newVerts[2].flags = VERTEX_CMD_EOL;

            aligned_vector_resize(&target->output->vector, target->output->vector.size - 1);
            aligned_vector_push_back(&target->output->vector, newVerts, 3);

            aligned_vector_resize(target->extras, target->extras->size - 1);
            aligned_vector_push_back(target->extras, newExtras, 3);
        } else {
            last->flags = VERTEX_CMD_EOL;
        }

    }
}

static inline void markDead(ClipVertex* vert) {
    vert->flags = VERTEX_CMD_EOL;
}

#define B000 0
#define B111 7
#define B100 4
#define B010 2
#define B001 1
#define B101 5
#define B011 3
#define B110 6

#define MAX_CLIP_TRIANGLES 255

void _glClipTriangleStrip(SubmissionTarget* target, uint8_t fladeShade) {
    static Triangle TO_CLIP[MAX_CLIP_TRIANGLES];
    static uint8_t CLIP_COUNT = 0;

    CLIP_COUNT = 0;

    ClipVertex* vertex = _glSubmissionTargetStart(target);
    const ClipVertex* end = _glSubmissionTargetEnd(target);
    const ClipVertex* start = vertex;

    int32_t triangle = -1;

    /* Go to the (potential) end of the first triangle */
    vertex++;

    uint32_t vi1, vi2, vi3;

    while(vertex < end) {
        vertex++;
        triangle++;

        uint8_t even = (triangle % 2) == 0;
        ClipVertex* v1 = (even) ? vertex - 2 : vertex - 1;
        ClipVertex* v2 = (even) ? vertex - 1 : vertex - 2;
        ClipVertex* v3 = vertex;

        /* Indexes into extras array */
        vi1 = v1 - start;
        vi2 = v2 - start;
        vi3 = v3 - start;

        /* Skip ahead if we don't have a complete triangle yet */
        if(v1->flags != VERTEX_CMD || v2->flags != VERTEX_CMD) {
            triangle = -1;
            continue;
        }

        uint8_t visible = ((v1->w > 0) ? 4 : 0) | ((v2->w > 0) ? 2 : 0) | ((v3->w > 0) ? 1 : 0);

        switch(visible) {
            case B111:
                /* All visible? Do nothing */
                continue;
            break;
            case B000:
                /*
                    It is not possible that this is any trangle except the first
                    in a strip. That's because:
                    - It's either the first triangle submitted
                    - A previous triangle must have been clipped and the strip
                      restarted behind the plane

                    So, we effectively reboot the strip. We mark the first vertex
                    as the end (so it's ignored) then mark the next two as the
                    start of a new strip. Then if the next triangle crosses
                    back into view, we clip correctly. This will potentially
                    result in a bunch of pointlessly submitted vertices.

                    FIXME: Skip submitting those verts
                */

                /* Even though this is always the first in the strip, it can also
                 * be the last */
                if(v3->flags == VERTEX_CMD_EOL) {
                    /* Wipe out the triangle */
                    markDead(v1);
                    markDead(v2);
                    markDead(v3);
                } else {
                    markDead(v1);
                    ClipVertex tmp = *v2;
                    *v2 = *v3;
                    *v3 = tmp;

                    triangle = -1;
                    v2->flags = VERTEX_CMD;
                    v3->flags = VERTEX_CMD;
                }
            break;
            case B100:
            case B010:
            case B001:
            case B101:
            case B011:
            case B110:
                assert(CLIP_COUNT < MAX_CLIP_TRIANGLES);

                /* Store the triangle for clipping */
                TO_CLIP[CLIP_COUNT].vertex[0] = *v1;
                TO_CLIP[CLIP_COUNT].vertex[1] = *v2;
                TO_CLIP[CLIP_COUNT].vertex[2] = *v3;

                TO_CLIP[CLIP_COUNT].extra[0] = *(VertexExtra*) aligned_vector_at(target->extras, vi1);
                TO_CLIP[CLIP_COUNT].extra[1] = *(VertexExtra*) aligned_vector_at(target->extras, vi2);
                TO_CLIP[CLIP_COUNT].extra[2] = *(VertexExtra*) aligned_vector_at(target->extras, vi3);

                TO_CLIP[CLIP_COUNT].visible = visible;
                ++CLIP_COUNT;

                /*
                    OK so here's the clever bit. If any triangle except
                    the first or last needs clipping, then the next one does aswell
                    (you can't draw a plane through a single triangle in the middle of a
                    strip, only 2+). This means we can clip in pairs which frees up two
                    vertices in the middle of the strip, which is exactly the space
                    we need to restart the triangle strip after the next triangle
                */
                if(v3->flags == VERTEX_CMD_EOL) {
                    /* Last triangle in strip so end a vertex early */
                    if(triangle == 0) {
                        // Wipe out the triangle completely
                        markDead(v1);
                        markDead(v2);
                    } else {
                        // End the strip
                        (vertex - 1)->flags = VERTEX_CMD_EOL;
                    }

                    markDead(vertex);

                    triangle = -1;
                } else if(triangle == 0) {
                    /* First triangle in strip, remove first vertex */
                    markDead(v1);

                    v2->flags = VERTEX_CMD;
                    v3->flags = VERTEX_CMD;

                    triangle = -1;
                } else {                    
                    /* FIXME: ?
                     * This situation doesn't actually seem possible, we always clip from one end
                     * of the triangle strip to the other, so we're never going to hit the plane in the
                     * middle of the strip (with previous/next unhandled tris).
                     *
                     * Uncomment if this actually happens */
                    assert(0 && "Not Implemented (see comment)");

                    /*
                    ClipVertex* v4 = vertex + 1;

                    TO_CLIP[CLIP_COUNT].vertex[0] = *v3;
                    TO_CLIP[CLIP_COUNT].vertex[1] = *v2;
                    TO_CLIP[CLIP_COUNT].vertex[2] = *v4;

                    visible = ((v3->w > 0) ? 4 : 0) | ((v2->w > 0) ? 2 : 0) | ((v4->w > 0) ? 1 : 0);

                    TO_CLIP[CLIP_COUNT].visible = visible;
                    ++CLIP_COUNT;

                    // Restart strip
                    triangle = -1;

                    // Mark the second vertex as the end of the strip
                    (vertex - 1)->flags = VERTEX_CMD_EOL;

                    if(v4->flags == VERTEX_CMD_EOL) {
                        markDead(vertex);
                        markDead(v4);
                    } else {
                        // Swap the next vertices to start a new strip
                        ClipVertex tmp = *vertex;
                        *vertex = *v4;
                        *v4 = tmp;

                        vertex->flags = VERTEX_CMD;
                        v4->flags = VERTEX_CMD;
                    } */
                }
            break;
            default:
                break;
        }
    }

    /* Now, clip all the triangles and append them to the output */
    GLushort i;
    for(i = 0; i < CLIP_COUNT; ++i) {
        _glClipTriangle(&TO_CLIP[i], TO_CLIP[i].visible, target, fladeShade);
    }
}