我如何使用 GTK 绘制像素图？

Question

我一直在尝试使用 GTK3 从内存缓冲区绘制像素图。我刚刚创建了一个内存缓冲区，并用 32 位 RGBA 格式的交替颜色行填充它。我一直在尝试以下功能： gdk_pixbuf_new_from_data(const guchar *data, GdkColorspace colorspace, gboolean has_alpha, int bits_per_sample, int width, int height, int rowstride, GdkPixbufDestroyNotify destroy_fn, gpointer destroy_fn_data)

使用它，我已经能够将内存缓冲区包装成 GdkPixbuf*，但是当我尝试将 pixbuf 绘制到 Cairo 屏幕时，图像似乎失真了。

这是我一直在试验的测试程序：

#include <gtk/gtk.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>

const int WIDTH = 1080;
const int HEIGHT = 720;

GtkWidget* mainWindow;

int currentCol = 0;

uint32_t* framebuffer = NULL;
GdkPixbuf* pixbuf = NULL;


typedef struct _rgbColor {
    uint8_t red;
    uint8_t green;
    uint8_t blue;
    uint8_t alpha;
}rgbColor;


void onWindowDestroy (GtkWidget* object, gpointer user_data) {
    gtk_main_quit();
}

gboolean onTimerTick(gpointer user_data) {
    rgbColor c = {0, 0, 0, 255};
    if (currentCol == 0) {
        c.red = 255;
    }
    if (currentCol == 1) {
        c.green = 255;
    }
    if (currentCol == 2) {
        c.blue = 255;
        currentCol = -1;
    }
    currentCol++;
    fillWithColour(framebuffer, c);

    rgbColor c1 = {0, 0, 255, 255};
    fillEveryInterval(framebuffer, c1, 20);
    gtk_widget_queue_draw(mainWindow);
    return 1;
}

gboolean onDraw(GtkWidget* widget, cairo_t *cr, gpointer user_data) {
    gdk_cairo_set_source_pixbuf(cr, pixbuf, 0, 0);
    cairo_paint(cr);
    return 0;
}

void fillWithColour(uint32_t* fb, rgbColor c) {
    for (int y = 0; y < HEIGHT; y++) {
        for (int x = 0; x < WIDTH; x++) {
            encodePixel(fb, c, x, y);
        }
    }
}

void fillEveryInterval(uint32_t* fb, rgbColor c, int interval) {
    for (int y = 1; y < HEIGHT; y += interval) {
        for (int x = 0; x < WIDTH; x++) {
            encodePixel(fb, c, x, y);
        }
    }
}


void encodePixel(uint32_t* fb, rgbColor c, int x, int y) {
    uint32_t r, g, b, a;

    r = c.red;
    g = c.green << 8;
    b = c.blue << 16;
    a = c.alpha << 24;
    
    *(fb + (sizeof(uint32_t)*y+x)) = b | g | r | a;
}

int main() {
    framebuffer = malloc(sizeof(uint32_t)*WIDTH*HEIGHT);
    rgbColor c = {255, 0, 0, 255};
    fillWithColour(framebuffer, c);


    gtk_init(NULL, NULL);
    mainWindow = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_default_size(GTK_WINDOW(mainWindow), WIDTH, HEIGHT);
    gtk_window_set_title(GTK_WINDOW(mainWindow), "Framebuffer test");

    GtkWidget* drawingArea = gtk_drawing_area_new();

    gtk_container_add(GTK_CONTAINER(mainWindow), drawingArea);

    g_signal_connect(GTK_WINDOW(mainWindow), "destroy", (GCallback)onWindowDestroy, NULL);
    g_signal_connect(GTK_DRAWING_AREA(drawingArea), "draw", (GCallback)onDraw, NULL);

    g_timeout_add(500, onTimerTick, NULL);

    gtk_widget_show_all(GTK_WINDOW(mainWindow));
    pixbuf = gdk_pixbuf_new_from_data(framebuffer, GDK_COLORSPACE_RGB, true, 8, WIDTH, HEIGHT, WIDTH*4, NULL, NULL);
    gtk_main();
}

我似乎无法弄清楚是什么导致了这个问题，我已经尝试过消除 alpha 通道并将 RGB 值打包成 24 位，但是我也没有成功地使用该方法。我认为这可能与 rowstride 有关，但是我无法找到可以解决该问题的值。我走在正确的轨道上，还是有更好的方法使用 GTK 将 RGB 缓冲区绘制到屏幕？

Answer 1

您只是将像素存储在了错误的位置。在 encodePixel 中，更改此行：

*(fb + (sizeof(uint32_t)*y+x)) = b | g | r | a;`

至此

fb[WIDTH*y+x] = b | g | r | a;

旁注：你应该对编译器发出的许多警告采取一些措施。

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