HQCommon.hh

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#ifndef HQCOMMON_HH
#define HQCOMMON_HH
 
#include "endian.hh"
#include "narrow.hh"
#include "xrange.hh"
#include <cassert>
#include <cstdint>
#include <span>
 
namespace openmsx {
 
struct EdgeHQ
{
        [[nodiscard]] inline bool operator()(uint32_t c1, uint32_t c2) const
        {
                if (c1 == c2) return false;
 
                unsigned r1 = (c1 >>  0) & 0xFF;
                unsigned g1 = (c1 >>  8) & 0xFF;
                unsigned b1 = (c1 >> 16) & 0xFF;
 
                unsigned r2 = (c2 >>  0) & 0xFF;
                unsigned g2 = (c2 >>  8) & 0xFF;
                unsigned b2 = (c2 >> 16) & 0xFF;
 
                auto dr = narrow_cast<int>(r1 - r2);
                auto dg = narrow_cast<int>(g1 - g2);
                auto db = narrow_cast<int>(b1 - b2);
 
                int dy = dr + dg + db;
                if (dy < -0xC0 || dy > 0xC0) return true;
 
                if (int du = dr - db;
                    du < -0x1C || du > 0x1C) return true;
 
                if (int dv = 3 * dg - dy;
                    dv < -0x30 || dv > 0x30) return true;
 
                return false;
        }
};
 
struct EdgeHQLite
{
        [[nodiscard]] inline bool operator()(uint32_t c1, uint32_t c2) const
        {
                return c1 != c2;
        }
};
 
template<typename EdgeOp>
void calcEdgesGL(std::span<const uint32_t> curr, std::span<const uint32_t> next,
                 std::span<Endian::L32> edges2, EdgeOp edgeOp)
{
        // Consider a grid of 3x3 pixels, numbered like this:
        //    1 | 2 | 3
        //   ---A---B---
        //    4 | 5 | 6
        //   ---C---D---
        //    7 | 8 | 9
        // Then we calculate 12 'edges':
        // * 8 star-edges, from the central pixel '5' to the 8 neighboring pixels.
        //   Let's call these edges 1, 2, 3, 4, 6, 7, 8, 9 (note: 5 is skipped).
        // * 4 cross-edges, between pixels (2,4), (2,6), (4,8), (6,8).
        //   Let's call these respectively A, B, C, D.
        // An edge between two pixels means the color of the two pixels is sufficiently distant.
        // * For the HQ scaler see 'EdgeHQ' for the definition of this distance function.
        // * The HQlite scaler uses a much simpler distance function.
        //
        // We store these 12 edges in a 16-bit value and order them like this:
        // (MSB (bit 15) on the left, LSB (bit 0) on the left, 'x' means bit is not used)
        //   || B 3 6 9 | D 2 x x || 8 1 A 4 | C 7 x x ||
        // This order has two important properties:
        // * The 12 bits are split in 2 groups of 6 bits and each group is MSB
        //   aligned within a byte. This allows to upload this data as a
        //   openGL texture and interpret each texel as a vec2 which
        //   represents a texture coordinate in another 64x64 texture.
        // * This order allows to calculate the edges incrementally:
        //   Suppose we already calculated the edges for the pixel immediate
        //   above and immediately to the left of the current pixel. Then the edges
        //        (1, 2, 3, A, B) can be calculated as:  (upper << 3) & 0xc460
        //    and (4, 7, C)       can be calculated as:  (left  >> 9) & 0x001C
        //   And only edges (6, 8, 9, D) must be newly calculated for this pixel.
        //   So only 4 new edges per pixel instead of all 12.
        //
        // This function takes as input:
        // * an in/out-array 'edges2':
        //   This contains the edge information for the upper row of pixels.
        //   And it gets update in-place to the edge information of the current
        //   row of pixels.
        // * 2 rows of input pixels: the middle and the lower pixel rows.
        // * An edge-function (to distinguish 'hq' from 'hqlite').
 
        auto size = curr.size();
        assert(next.size() == size);
        assert(2 * edges2.size() == size);
 
        using Pixel = uint32_t;
 
        uint32_t pattern = 0;
        Pixel c5 = curr[0];
        Pixel c8 = next[0];
        if (edgeOp(c5, c8)) pattern |= 0x1800'0000; // edges: 9,D (right pixel)
 
        auto size2 = size / 2;
        for (auto xx : xrange(size2 - 1)) {
                pattern = (pattern >> (16 + 9)) & 0x001C;   // edges: 6,D,9 -> 4,7,C        (left pixel)
                pattern |= (edges2[xx] << 3) & 0xC460'C460; // edges C,8,D,7,9 -> 1,2,3,A,B (left and right)
 
                if (edgeOp(c5, c8)) pattern |= 0x0000'0080; // edge: 8 (left)
                Pixel c6 = curr[2 * xx + 1];
                if (edgeOp(c6, c8)) pattern |= 0x0004'0800; // edge: D (left), 7 (right)
                if (edgeOp(c5, c6)) pattern |= 0x0010'2000; // edge: 6 (left), 4 (right)
                Pixel c9 = next[2 * xx + 1];
                if (edgeOp(c5, c9)) pattern |= 0x0008'1000; // edge: 9 (left), C (right)
 
                if (edgeOp(c6, c9)) pattern |= 0x0080'0000; // edge:           8 (right)
                c5 = curr[2 * xx + 2];
                if (edgeOp(c5, c9)) pattern |= 0x0800'0000; // edge:           D (right)
                if (edgeOp(c6, c5)) pattern |= 0x2000'0000; // edge:           6 (right)
                c8 = next[2 * xx + 2];
                if (edgeOp(c6, c8)) pattern |= 0x1000'0000; // edge:           9 (right)
 
                edges2[xx] = pattern;
        }
 
        pattern = (pattern >> (16 + 9)) & 0x001C;    // edges: 6,D,9 -> 4,7,C         (left pixel)
        pattern |= (edges2[size2 - 1] << 3) & 0xC460'C460; // edges: C,8,D,7,9 -> 1,2,3,A,B (left and right)
 
        if (edgeOp(c5, c8)) pattern |= 0x0000'0080;  // edge: 8 (left)
        Pixel c6 = curr[size - 1];
        if (edgeOp(c6, c8)) pattern |= 0x0004'0800;  // edge: D (left), 7 (right)
        if (edgeOp(c5, c6)) pattern |= 0x0010'2000;  // edge: 6 (left), 4 (right)
        Pixel c9 = next[size - 1];
        if (edgeOp(c5, c9)) pattern |= 0x0008'1000;  // edge: 9 (left), C (right)
 
        if (edgeOp(c6, c9)) pattern |= 0x1880'0000;  // edges:      8,9,D (right)
 
        edges2[size2 - 1] = pattern;
}
 
} // namespace openmsx
 
#endif