Question

我有此代码：

var rules = [{"operator":null,"conditionString":"x == y"},{"operator":"and","conditionString":"x > y"},{"operator":"or","rules":[{"operator":null,"conditionString":"x <= y"},{"operator":"and","conditionString":"x > y"},{"operator":"and","rules":[{"operator":null,"conditionString":"x < y"},{"operator":"or","conditionString":"x != y"}]},{"operator":"and","conditionString":"x == y"}]},{"operator":"and","conditionString":"x >= y"}]

function process(rules) {
  return rules.reduce((r, e, i) => {
    let nested = ''
    let op = '';
    let cond = '';

    if (e.rules) {
      nested = process(e.rules);
    }

    if (e.conditionString) {
      cond = e.conditionString
    }
		
    if(i === 0) op = '';
    else if (e.operator === 'and') op = '&&';
    else if (e.operator === 'or') op = '||';

    r += (op ? ` ${op} ` : '') + cond + (nested ? `(${nested})` : '')

    return r;
  }, '')
}

const result = process(rules);
console.log(result)

写方法的主要部分

void PngWriteCallback(png_structp  png_ptr, png_bytep data, png_size_t length)
{
    std::vector<uint8_t> *p = (std::vector<uint8_t>*)png_get_io_ptr(png_ptr);
    if (p->capacity() <= p->size() + length + 1)
    {
        p->resize(p->size() + length + 1);
    }
    p->insert(p->end(), data, data + length);
}

但是，程序因以下原因而崩溃：

png_set_IHDR(png_ptr,
    info_ptr,
    w,
    h,
    8,
    PNG_COLOR_TYPE_GRAY,
    PNG_INTERLACE_NONE,
    PNG_COMPRESSION_TYPE_DEFAULT,
    PNG_FILTER_TYPE_DEFAULT);

png_byte ** row_pointers = (png_byte **)png_malloc(png_ptr, h * sizeof(png_byte *));
for (size_t y = 0; y < h; y++)
{
    row_pointers[y] = (png_byte *)(data + w * y);
}
png_set_rows(png_ptr, info_ptr, row_pointers);


std::vector<uint8_t> out;
out.reserve(w * h * 4);
png_set_write_fn(png_ptr, &out, PngWriteCallback, NULL);

png_set_compression_strategy(png_ptr, Z_HUFFMAN_ONLY);
png_write_png(png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, NULL);

std::vector<uint8_t> out1 = std::move(out);
out.clear();
out.reserve(w * h * 4);

png_set_compression_strategy(png_ptr, Z_FILTERED);
png_write_png(png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, NULL);

if (out.size() < out1.size())
{
    printf("Huffman %d vs %d\n", out.size(), out1.size());
    fwrite(out.data(), sizeof(uint8_t), out.size(), fp);
}
else 
{
    printf("Z_FILTER %d vs %d\n", out1.size(), out.size());
    fwrite(out1.data(), sizeof(uint8_t), out1.size(), fp);
}

//==============================================================

png_free(png_ptr, row_pointers);

在第二个呼叫libpng warning: zstream not in use (internal error) libpng error: stream error上。

如何用不同的设置两次写入文件？如果我省略第二个png_write_png，则一切正常。

LibPng-使用不同的设置两次写入图像

0 个答案: