c - 使用 Cairo 和 C 旋转和合成 PNG 文件

Question

我正在使用 C 中的 Cairo 编写一个应用程序，该应用程序执行以下操作:

• 加载背景 PNG(轮子)
• 将轮子旋转 90 度
• 在轮子上绘制来自其他 PNG 文件的一组数字
• 这样做，直到轮盘的所有 6 个部分都绘制了轮盘上的数字
• 将 PNG 保存到文件 ( results.png )

我遇到的问题是，如果我不旋转轮子，数字就会正确绘制，如image所示。 ，除非轮子没有根据需要旋转。

但是，如果我尝试旋转并在轮子上绘制数字，我会得到一个没有数字的旋转轮子，如 image. 中所示。

我尝试了代码的各种排列，但似乎无法使其工作。我希望得到一些提示和/或示例代码来显示我做错了什么。我检查了 Cairo 文档，但没有结果。

代码可以找到here.

这里:

#include <cairo.h>
#include <stdio.h>
#include <string.h>
#include <math.h>


typedef struct
{
    int numImages;      /* Number of images in win amount string */
    int indexes[7];     /* indexes into NumberImages[] */
}WinAmountData;

/***** Function Prototypes *****************/
int InitImages( void );
void DestroyNumberImages( void );
int ParseWinAmountString( char *string, WinAmountData *amtData );
int Rotate( cairo_t *cr , cairo_surface_t *image, double degrees );
/*******************************************/


typedef struct
{
    int xOffset;    /* pixel count offsete before next digit */
    char fileName[20];
    cairo_surface_t *image; 
}ImageInfo;

ImageInfo NumberImages[] =
{
    { 8, "images/0.png", NULL },
    { 10, "images/1.png", NULL },
    { 10, "images/2.png", NULL },
    { 10, "images/3.png", NULL },
    { 10, "images/4.png", NULL },
    { 10, "images/5.png", NULL },
    { 10, "images/6.png", NULL },
    { 10, "images/7.png", NULL },
    { 10, "images/8.png", NULL },
    { 10, "images/9.png", NULL },
    { 7, "images/$.png", NULL },
    { 10, "images/euro.png", NULL },
    { 7, "images/pound.png", NULL },
    { 7, "images/yen.png", NULL }
};

enum { DOLLAR = 10, EURO, POUND, YEN };

#define FALSE 0
#define TRUE 1

int InitImages( void )
{
    int i;
    int ret = TRUE;
    cairo_status_t imgStatus;


    for( i = 0; i < ( sizeof( NumberImages ) / sizeof( ImageInfo ) ) && ret == TRUE; i++ )
    {
        NumberImages[i].image = cairo_image_surface_create_from_png( NumberImages[i].fileName );    
        imgStatus = cairo_surface_status(NumberImages[i].image);
        ret = ( CAIRO_STATUS_SUCCESS == imgStatus );
    }

    return( ret );
}


void DestroyNumberImages( void )
{
    int i;

    for( i = 0; i < ( sizeof( NumberImages ) / sizeof( ImageInfo ) ); i++ )
    {
        cairo_surface_destroy(NumberImages[i].image);
    }

    return;
}

int ParseWinAmountString( char *string, WinAmountData *amtData )
{
    int ret = TRUE;
    int i = 0, len;

    len = strlen( string );
    if( (len > 0) && (len < 8) )
    {
        amtData->numImages = len;

        for( i = 0; i < amtData->numImages && TRUE == ret; i++ )
        {
            if( string[i] >= '0' && string[i] <= '9' )
            {
                amtData->indexes[i] = string[i] - '0';
            }
            else
            {
                switch( string[i] )
                {
                    case 'D':
                        amtData->indexes[i] = DOLLAR;
                    break;

                    case 'Y':
                        amtData->indexes[i] = YEN;
                    break;

                    case 'E':
                        amtData->indexes[i] = EURO;
                    break;

                    case 'P':
                        amtData->indexes[i] = POUND;
                    break;

                    default:
                        ret = FALSE;
                    break;
                }
            }
        }
    } 
    else
    {
        ret = FALSE;
    }   

    return( ret );
}

double DegreesToRadians( double degrees )
{
    return((double)((double)degrees * ( (double)M_PI/(double)180.0 )));
}

int Rotate( cairo_t *cr , cairo_surface_t *image, double degrees )
{
    int ret = 0;

    cairo_translate(cr, 90, 90);
    cairo_rotate(cr, DegreesToRadians( degrees ));
    cairo_set_source_surface(cr, image, -90, -90);

    cairo_paint(cr);

    return ( ret );
}


int main(int argc, char *argv[])
{
    int i,x,y;
    cairo_surface_t *imgWheelBg = NULL;
    WinAmountData amtData;


    if( argc == 2 )
    {
        printf("Parsing [%s]\n", argv[1]);
        if ( ParseWinAmountString( argv[1], &amtData ) == TRUE )
        {
            printf("Amount indexes = [ ");
            for( i = 0; i < amtData.numImages; i++ )
            {
                printf("%d ", amtData.indexes[i]);
            }
            printf("]\n");
        }
        else
        {
            printf("Failed to parse amount.\n");
            return( 1 );
        }
    }
    else
    {
        printf("Usage: %s <Amount String>\n", argv[0]);
        return( 1 );
    }

    if( InitImages() == TRUE )
    {
        imgWheelBg = cairo_image_surface_create_from_png("images/blankwheel.png");

        //Create the background image
        cairo_surface_t *imgResult = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, 180, 180);

        //Create the cairo context
        cairo_t *cr = cairo_create(imgResult);

        //Paint empty wheel image
        cairo_set_source_surface(cr, imgWheelBg, 0, 0);
        cairo_paint(cr);

        // At this point the wheel is painted ( blankwheel.png )

        // vvvvvvvvvv THIS PART SEEMS TO BE CAUSING TROUBLES vvvvvvvvvv     

        // With this call the wheel DOES get rotated 90 degress. Confirmed
        // by viewing the resulting PNG file. 
        // HOWEVER, after the Rotate() is called the numbers aren't put on the wheel.
        // if I remove the Rotate() call, the wheel is drawn, not rotated, but the
        // numbers are properly composited over the image.

        //Rotate( cr, imgWheelBg, 90 );

        // ^^^^^^^^^^^ THIS PART SEEMS TO BE CAUSING TROUBLES ^^^^^^^^^^^       

        /* Set drawing begin point in pixels */
        x = 101;
        y = 82;

        /* Draw all characters in win amount string */
        for( i = 0; i < amtData.numImages; i++ )
        {
            cairo_set_source_surface(cr, NumberImages[amtData.indexes[i]].image, x, y);
            cairo_paint(cr);
            x += NumberImages[i].xOffset;
        }

        //Destroy the cairo context and/or flush the destination image
        cairo_surface_flush(imgResult);
        cairo_destroy(cr);

        //And write the results into a new file
        cairo_surface_write_to_png(imgResult, "result.png");

        // Destroy resources
        cairo_surface_destroy(imgResult);
        cairo_surface_destroy(imgWheelBg);
        DestroyNumberImages();
        printf("SUCCESS\n");
    }
    else
    {
        printf("FAILED Init Images\n");
    }

    return 0;
}

编辑:最终目标是生成图像 like this one以编程方式在 GTK 应用程序中根据需要实时制作动画。

编辑:来自 Mikhail Kozhevnikov 的评论和 Uli Schlachter我能够使用 this code 找到解决方案.

非常感谢!

Answer 1

我认为问题在于，变换应用于所有内容，包括数字图像，并且由于这种变换，它们被绘制在图片之外的某个地方。我建议the matrix be stored在应用转换之前和 restored画完圆之后。或者您希望数字也旋转吗？..