在 SDL2 中垂直翻转表面

如何解决在 SDL2 中垂直翻转表面

我得到的最接近的是这个：

for dist in data["dcode"].unique():
    d_data = data[data["dcode"] == dist]
    #print(dist)
    for block in d_data["mandal"].unique():
        prev_rain = 0
        prev_to_date = "01/12/2022"
        for each in rain_dev_input:
            #[(rain_dev_input["TERM"] == "DEFICIT RAINFALL") & (rain_dev_input["disT_CODE"] == 240)]:
            #print(each)
            distcode = each["disT_CODE"]
            #print(distcode)
            term = str(each["TERM"])
            if (distcode == dist) & (term == "EXCESS RAINFALL"):
                start_date = each["FROM_PERIOD"]
                end_date = each["TO_PERIOD"]
                s_date = datetime.datetime.strptime(start_date,"%d/%m/%y")
                e_date = datetime.datetime.strptime(end_date,"%d/%m/%y")
                #s_date = start_date.strftime(start_date,"%Y-%m-%d")
                #e_date = end_date.strftime(end_date,"%Y-%m-%d")
                #count1 = daterange(s_date,e_date)
                #print(s_date,": ",e_date)

                m_data = d_data[d_data["mandal"] == block]
                p_data = m_data.loc[start_date:end_date]
                for singledate in daterange(s_date,e_date):
                    #print("Inside Excess Rain")
                    from_date = datetime.datetime.strftime(singledate,"%Y-%m-%d")
                    to_date = datetime.datetime.strftime(
                        (singledate + timedelta(2)),"%Y-%m-%d"
                    )
                    total_rain = p_data.loc[from_date:to_date]["rain"].sum()
                    #print(total_rain)
                    range1 = float(each["RANGE1"])
                    range2 = float(each["RANGE2"])

                    if (total_rain >= range1) & (total_rain < range2):
                        #print("inside write to file")
                        if (from_date <= prev_to_date <= to_date) & (prev_rain <= total_rain):
                            temp["Max"] = total_rain;

                        prev_rain = total_rain
                        prev_to_date = to_date
                        temp = dict()
                        temp["district"] = each["disT_NAME"]
                        temp["mandal"] = block
                        temp[
                            "category"
                        ] = "excess rainfall for 3 consecutive days,cumulative"
                        temp["rainfall"] = total_rain
                        temp["from_date"] = from_date
                        temp["to_date"] = to_date
                        temp["phase"] = each["PHASE"]
                        #temp["insurance"] = insurance_excessrain(each,total_rain)
                        temp["insurance"] = (total_rain - range1)* each["PAYOUT"]
                        excess_rainfall.append(temp)
# %%
# output excess rainfall rain_dev_list data
excess_rain = pd.DataFrame(excess_rainfall)
excess_rain.to_csv(str(output_folder) + "/excess_rainfall_2020_h2.csv",index=False)

但它并没有保持透明度。我如何才能真正实现这一目标？

解决方法

我不知道错误到底在哪里，我在我的机器上尝试了你的代码，它在我使用的图像上运行良好。我怀疑您的代码确实保留了透明度，但稍后在您的实现中将其删除。

无论如何，如果我可以建议对您的代码进行改进：您不需要如此复杂的操作来垂直翻转表面。 SDL_Surface 结构以行优先顺序存储像素数据，这意味着 pixels 数组是一系列行，其中每一行的大小为 pitch 字节。因此，要垂直翻转您的表面，您可以简单地遍历行并交换它们。这种方法的优点是不需要了解像素格式，因此可以对所有图像类型（alpha 通道或非 alpha 通道）实现，并且实现起来非常简单。

这是一个您可以编译和试验的最小示例：

#include <SDL2/SDL.h>
#include <SDL2/SDL_image.h>

void flip_surface(SDL_Surface* surface) 
{
    SDL_LockSurface(surface);
    
    int pitch = surface->pitch; // row size
    char* temp = new char[pitch]; // intermediate buffer
    char* pixels = (char*) surface->pixels;
    
    for(int i = 0; i < surface->h / 2; ++i) {
        // get pointers to the two rows to swap
        char* row1 = pixels + i * pitch;
        char* row2 = pixels + (surface->h - i - 1) * pitch;
        
        // swap rows
        memcpy(temp,row1,pitch);
        memcpy(row1,row2,pitch);
        memcpy(row2,temp,pitch);
    }
    
    delete[] temp;

    SDL_UnlockSurface(surface);
}

int main(int argc,char* argv[]) 
{
    SDL_Init(SDL_INIT_VIDEO);
    
    SDL_Surface* surface = IMG_Load("image.png");
    flip_surface(surface);
    IMG_SavePNG(surface,"result.png");
    
    SDL_Quit();
    
    return 0;
}