Emboss a cairo surface
This sample shows how to apply an emboss effect to a cairo A8 image surface.
/*
Adapted from "Fast Embossing Effects on Raster Image Data"
Original code by: John Schlag, <jfs@kerner.com>
Adapted code by: Jeremy Moles, <cubicool@gmail.com>
Found in the publication "Graphics Gems IV", Academic Press, 1994
*/
#include <cairo.h>
#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define PIXEL_SCALE 255
#define WIDTH_45 1
/* This function will use an exisiting surface's data and create and NEW surface copy
// of that data which has the emboss lighting algorithm applied to it. */
static cairo_surface_t* _create_embossed_surface_from_surface(
cairo_surface_t* surface,
double azimuth,
double elevation
) {
unsigned char* src = cairo_image_surface_get_data(surface);
unsigned int width = cairo_image_surface_get_width(surface);
unsigned int stride = cairo_image_surface_get_stride(surface);
unsigned int height = cairo_image_surface_get_height(surface);
cairo_surface_t* dstSurface = cairo_image_surface_create(CAIRO_FORMAT_A8, width, height);
unsigned char* dst = cairo_image_surface_get_data(dstSurface);
/* Compute the light vector from the input parameters.
// Normalize the length to PIXEL_SCALE for fast shading calculation. */
long Lx = cos(azimuth) * cos(elevation) * PIXEL_SCALE;
long Ly = sin(azimuth) * cos(elevation) * PIXEL_SCALE;
long Lz = sin(elevation) * PIXEL_SCALE;
long Nz = (6 * 255) / WIDTH_45;
long Nz2 = Nz * Nz;
long NzLz = Nz * Lz;
unsigned int y = 1;
unsigned int x = 1;
/* TODO: Would it be better to fill DST with SRC instead of the Lz value?
// memcpy(dst, src, stride * height); */
memset(dst, Lz, stride * height);
for(y = 1; y < height - 2; y++) {
for(x = 1; x < stride - 1; x++) {
unsigned int offset = (y * stride) + x;
unsigned char* s1 = src + offset;
unsigned char* s2 = s1 + stride;
unsigned char* s3 = s2 + stride;
unsigned char shade = 0;
/* Compute the normal from the source. The type of the expression
// before the cast is compiler dependent. In some cases the sum is
// unsigned, in others it is signed. Ergo, cast to signed. */
long Nx = (long)(s1[-1] + s2[-1] + s3[-1] - s1[1] - s2[1] - s3[1]);
long Ny = (long)(s3[-1] + s3[0] + s3[1] - s1[-1] - s1[0] - s1[1]);
long NdotL = Nx * Lx + Ny * Ly + NzLz;
/* Shade with distant light source. */
if(!Nx && !Ny) shade = Lz;
else if(NdotL < 0) shade = 0;
else shade = NdotL / sqrt(Nx * Nx + Ny * Ny + Nz2);
*(dst + offset) = shade;
}
}
return dstSurface;
}
/* This function only supports A8 surfaces at the moment, and delegates work to the
// similarly named function above. */
static cairo_surface_t* create_embossed_surface_from_surface(
cairo_surface_t* surface,
double azimuth,
double elevation
) {
if(cairo_image_surface_get_format(surface) != CAIRO_FORMAT_A8) {
printf("This example only supports embossing A8 surfaces.\n");
printf("It shouldn't be too wildy hard to add other format types.\n");
return 0;
}
else return _create_embossed_surface_from_surface(surface, azimuth, elevation);
}
int main(int argc, char** argv) {
unsigned int w = 400;
unsigned int h = 50;
unsigned int textSize = 35;
const char* text = "Cairo Emboss!!!";
cairo_surface_t* surface = cairo_image_surface_create(CAIRO_FORMAT_A8, w, h);
cairo_t* cr = cairo_create(surface);
cairo_text_extents_t extents;
if(argc != 3) {
printf(
"usage: %s <int> <int>\nThe two integral arguments passed in are "
"the light azimuth and elevation values, in angles.\n",
argv[0]
);
goto cleanup;
}
cairo_select_font_face(cr, "Sans", CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_BOLD);
cairo_set_font_size(cr, textSize);
cairo_text_extents(cr, text, &extents);
cairo_move_to(
cr,
((double)(w - extents.width) / 2.0f) - extents.x_bearing,
(double)(h - extents.y_bearing) / 2.0f
);
cairo_show_text(cr, text);
cairo_surface_t* emboss = create_embossed_surface_from_surface(
surface,
atoi(argv[1]) * (M_PI / 180.0f),
atoi(argv[2]) * (M_PI / 180.0f)
);
if(!emboss) {
printf("Calling the emboss function failed; cleaning up and leaving.\n");
goto cleanup;
}
cairo_surface_write_to_png(surface, "cairo_emboss_normal.png");
cairo_surface_write_to_png(emboss, "cairo_emboss_embossed.png");
printf("Wrote cairo_emboss_{normal,embossed}.png to your local directory.\n");
cairo_surface_destroy(emboss);
cleanup:
cairo_surface_destroy(surface);
cairo_destroy(cr);
return 0;
}