Function WriteVector

engine/graphics/src/graphics_vertices.cpp:281–311

Supports writing a vector to a scalar, matrix, or vector. Regardless of destination type, if we have fewer elements in the source vector than in the destination vector, the rest of the vector is filled with zeroes.

    // Regardless of destination type, if we have fewer elements in the source vector than in the destination vector,
    // the rest of the vector is filled with zeroes.
    static void WriteVector(uint8_t* write_ptr, const UnpackAttributeData& src_data, const UnpackAttributeData& dst_data)
    {
        const uint32_t num_src_elements_to_write  = dmMath::Min(src_data.m_ElementCount, dst_data.m_ElementCount);
        const uint32_t num_zero_elements_to_write = dst_data.m_ElementCount - num_src_elements_to_write;
        const uint32_t dst_element_byte_width     = DataTypeToByteWidth(dst_data.m_DataType);

        // Case 1: When src and dst data types match, just copy directly
        if (src_data.m_DataType == dst_data.m_DataType)
        {
            const uint32_t copy_size = num_src_elements_to_write * dst_element_byte_width;
            memcpy(write_ptr, src_data.m_ValuePtr, copy_size);
            write_ptr += copy_size; // Advance pointer
        }
        // Case 2: Convert source data type to float and then write to destination type
        else
        {
            const uint32_t src_element_byte_width = DataTypeToByteWidth(src_data.m_DataType);
            for (uint32_t i = 0; i < num_src_elements_to_write; ++i)
            {
                float float_value = VertexAttributeDataTypeToFloat(src_data.m_DataType, src_data.m_ValuePtr + i * src_element_byte_width);

                write_ptr = WriteVertexAttributeFromFloat(write_ptr, float_value, dst_data.m_DataType);
            }
        }

        // Zero out any remaining elements in the destination
        if (num_zero_elements_to_write > 0)
        {
            memset(write_ptr, 0, num_zero_elements_to_write * dst_element_byte_width);
        }
    }

    // Supports writing a single scalar as a scalar, matrix, or vector.
    // If the destination is a matrix, the value is written on the diagonal.