In this article I'll show how to make a CLI application to generate abstract wallpaper for your computer or smartphone using the CapyRandom and CapyBezier objects.

(The complete code is available at the end of the article)

The idea is as follow: create a palette of colors, paint the whole image with a 2D->3D Bezier to create a smooth background, then stroke many 1D->2D Beziers. The palette of colors is created as follow: a few base colors are selected randomly, and many other variations are created from these base colors by altering the saturation and value without touching the hue. The background's Bezier takes as input the scaled coordinates in the image, and return as output the RGB value of the pixel at that coordinates. Its control point values are the RGB value of some randomly choosen colors in the palette. Its order too is randomly selected. The foreground Beziers also have a random order. Each stroke is divided into several substrokes, each one with random size, pen's hardness, and variation of colors from the same base color. The control point are the 2D coordinates of the curve, randomly selected for each stroke and then randomly modified at each substroke. Parameters allow to control the amount of randomness and achieve a satisfying result.

First, lets define a structure to hold all the needed data.

// Structure to memorise the appli variables struct App { // Return code at the end of execution int ret; // Appli name char* name; // Parser to process the command line arguments CapyArgParser parser; // Flag for display bool flagDisplay; // Flag for monochrome bool flagGrey; // Display CapyDisplay display; // Random generator CapyRandom rng; // Result image and its dimensions CapyImgDims imgDims; CapyImgDims_t imgMinDim; CapyImgDims_t imgMaxDim; CapyImg img; // Color palette CapyColorData palette[NB_MAX_BASE_COLOR][NB_MAX_VARIATION_COLOR]; uint8_t nbColor; uint8_t nbVariationColor[NB_MAX_BASE_COLOR]; };

and a few constants to control the generation

// Constants #define NB_MAX_BASE_COLOR 4 #define NB_MAX_VARIATION_COLOR 10 #define AMPLITUDE_VARIATION_COLOR 0.1 #define MAX_ORDER_BG 5 #define NB_MAX_STROKE 20 #define MIN_SIZE_PEN (app->imgMinDim / 50) #define MAX_SIZE_PEN (app->imgMaxDim / 25) #define MAX_ORDER_FG ((app->imgMinDim / 100) + 2) #define NB_MIN_SUBSTROKE 5 #define NB_MAX_SUBSTROKE 15

and a few shortcuts.

// Shortcuts #define RNG &(app->rng) #define RANGE_NB_MAX_COLOR \ (CapyRangeUInt8){ .min=1, .max=NB_MAX_BASE_COLOR } #define RANGE_NB_MAX_VARIATION \ (CapyRangeUInt8){ .min=1, .max=NB_MAX_VARIATION_COLOR } #define RANGE_VARIATION_COLOR \ (CapyRangeDouble){ \ .min=-0.5*AMPLITUDE_VARIATION_COLOR, \ .max= 0.5*AMPLITUDE_VARIATION_COLOR } #define RANGE_ORDER_BG \ (CapyRangeUInt8){ .min=1, .max=MAX_ORDER_BG } #define RANGE_IDX_COLOR \ (CapyRangeUInt8){ .min=0, .max=app->nbColor-1 } #define RANGE_IDX_VARIATION(i) \ (CapyRangeUInt8){ .min=0, .max=app->nbVariationColor[i]-1 } #define RANGE_NB_STROKE \ (CapyRangeUInt64){ .min=1, .max=NB_MAX_STROKE } #define RANGE_SIZE_PEN \ (CapyRangeDouble){ .min=MIN_SIZE_PEN, .max=MAX_SIZE_PEN } #define RANGE_STROKE_ORDER \ (CapyRangeUInt8){ .min=2, .max=MAX_ORDER_FG } #define RANGE_NB_SUBSTROKE \ (CapyRangeUInt8){ .min=NB_MIN_SUBSTROKE, .max=NB_MAX_SUBSTROKE } #define RANGE_HARDNESS \ (CapyRangeUInt8){ .min=capyPenHardness_9H, .max=capyPenHardness_HB } #define RANGE_SIZE_VARIATION \ (CapyRangeDouble){ .min=-MIN_SIZE_PEN*5, .max=MIN_SIZE_PEN*5 } #define RANGE_CTRL_VARIATION \ (CapyRangeDouble){ .min=-2.0*size, .max=2.0*size } #define RANGE_POS(i) \ (CapyRangeDouble){ .min=-size, .max=app->imgDims.dims[i]+size } #define RANGE_ALPHA \ (CapyRangeDouble){ .min=0.1, .max=1.0 } #define REFRESH_DISPLAY \ if (app->flagDisplay) $(&(app->display), copyImg)(&(app->img))

Exception management is simple, there is only the case for invalid image dimensions to care about.

// App exceptions enum AppExceptions { excInvalidSize = CapyExc_LastID, lastAppException }; // Label for the AppExceptions char* exceptionStr[] = { "Invalid size for the image", }; char const* ExcToStr(int16_t exc) { // If the exception ID is one of AppExceptions, // return the exception's explanation if (exc >= excInvalidSize && exc < lastAppException) return exceptionStr[exc - excInvalidSize]; // Else, the exception ID is not one of AppExceptions, return NULL else return NULL; }

The base of the main function is the same as usual:

// Main function int main( int argc, char** argv) { // Set the conversion function for raised exceptions CapyAddExcToStrFun(ExcToStr); // Instance of the application struct App app; // Initialise the return value app.ret = EXIT_SUCCESS; try { ... } catchDefault { // Inform the user about the raised exception $(&capyDecoratorRed, fprintf)( stdout, "Sorry, an exception occured. Exiting.\n"); $(&capyDecoratorRed, fprintf)( stdout, "%s\n", CapyExcToStr(CapyGetLastExcId())); app.ret = EXIT_FAILURE; } endCatch; return app.ret; }

and the try block looks as follow. First, define the command line interface of the appli.

// Definition of the arguments from the command line CapyArg args[] = { {.lbl=argv[0], .nbVal=3, .help="Generate random background images with Bezier curves.\n" "Takes 3 mandatory arguments: <width> <height> <path>\n" "During display of the result, press space to generate " "a new image."}, {.shortLbl="-s", .lbl="--seed", .nbVal=1, .help="Seed for the pseudo-RNG (current time by default)"}, {.shortLbl="-d", .lbl="--display", .nbVal=capyArg_noVal, .help="Display the generated image"}, {.shortLbl="-m", .lbl="--monochrome", .nbVal=capyArg_noVal, .help="Use a greyscale palette"}, };

then parse and check the arguments

// Create the argument parser and parse the arguments app.parser = CapyArgParserCreate(argc, argv, args); // Check the requested dimensions app.name = argv[0]; app.imgDims.width = $(&(app.parser), getAsInt)(app.name, 0); app.imgDims.height = $(&(app.parser), getAsInt)(app.name, 1); if (app.imgDims.width <= 0 || app.imgDims.height <= 0) raiseExc(excInvalidSize); // Memorise the appli name and min/max dimensions app.imgMaxDim = (app.imgDims.width > app.imgDims.height ? app.imgDims.width : app.imgDims.height); app.imgMinDim = (app.imgDims.width < app.imgDims.height ? app.imgDims.width : app.imgDims.height); // Initialise the random generator with the given seed or the // current time int64_t seed = time(NULL); if ($(&(app.parser), isSet)("-s")) seed = $(&(app.parser), getAsInt)("-s", 0); app.rng = CapyRandomCreate(seed); // Set the flags app.flagDisplay = $(&(app.parser), isSet)("-d"); app.flagGrey = $(&(app.parser), isSet)("-m");

Once this is done, the generation can be performed. A CapyDisplay is used to display the image during generation and let the user interacts with the appli.

// If the user requested display during generation if (app.flagDisplay) { // Create the display CapyDisplay d = CapyDisplayCreate(&(app.imgDims), app.name); memcpy(&(app.display), &d, sizeof(CapyDisplay)); $(&(app.display), show)(); // Wait for the display to be ready while ($(&(app.display), isDisplayed)() == false); } // Generate the image GenerateImg(&app); // If the user requested display during generation if (app.flagDisplay) { // Wait until the display has been closed while ($(&(app.display), isDisplayed)()) { // Update the displayed image $(&(app.display), copyImg)(&(app.img)); // Slow down the display as their is nothing in particular to // do but wait CapySleepMs(1000); // Listen to events CapyDisplayKeyEvt evt = $(&(app.display), getKeyPressed)(); // If the user requested to close the display, do it if (evt.keyval == GDK_KEY_q) $(&(app.display), close)(); // If the user requested to generate a new image, do it else if (evt.keyval == GDK_KEY_space) GenerateImg(&app); } } // Save the result image char* pathImg = $(&(app.parser), getAsStr)(app.name, 2); $(&(app.img), saveToPathAsPNG)(pathImg); // Destruct the display if necessary if (app.flagDisplay) CapyDisplayDestruct(&(app.display));

The generation is divided into the creation of the palette, the background generation and the foreground generation.

// Generate the image void GenerateImg(struct App* const app) { // Update the status in the title bar if (app->flagDisplay) $(&(app->display), setTitle)("generating..."); // Create the image app->img = CapyImgCreate(capyImgMode_rgb, app->imgDims); // Create the color palette CreateColorPalette(app); // Create the background CreateBackground(app); // Create the foreground CreateForeground(app); // Update the status in the title bar if (app->flagDisplay) $(&(app->display), setTitle)(app->name); }

The palette is stored in a two dimensional array to make it easy to use later. The first index will be the base color index and the second index will be the variation.

// Create the color palette void CreateColorPalette(struct App* const app) { // Set the number of colors and the number of their variations app->nbColor = $(RNG, getUInt8Range)(&RANGE_NB_MAX_COLOR); loop (iColor, app->nbColor) app->nbVariationColor[iColor] = $(RNG, getUInt8Range)(&RANGE_NB_MAX_VARIATION); // Loop on the base colors loop (iColor, app->nbColor) { ... } }

The base color selection consists simply of setting the three RGB values at random. If the user requested a grey image these 3 values are forced to the same one.

// Select the base color CapyColorData baseColor = capyColorRGBAWhite; loop (i, 3) baseColor.rgb[i] = $(RNG, getDouble)(); if (app->flagGrey) baseColor.rgb[0] = baseColor.rgb[1] = baseColor.rgb[2];

The variations are obtained by converting the base color RGB to HSV (to be able to transform it without modifying the hue), randomly modifying the saturation and value, and converting it back to RGB.

// Loop on the variations loop (jColor, app->nbVariationColor[iColor]) { // Convert the base color from rgb to hsv CapyColor color = CapyColorCreate(baseColor); CapyColorData hsv = $(&color, rgb2hsv)(); // Create a variation by altering the saturation and value only loop (i, 2) { hsv.hsv[i + 1] += $(RNG, getDoubleRange)(&RANGE_VARIATION_COLOR); if (hsv.hsv[i + 1] < 0.0) hsv.hsv[i + 1] = 0.0; if (hsv.hsv[i + 1] > 1.0) hsv.hsv[i + 1] = 1.0; } // Set the variation in the palette color.vals = hsv; app->palette[iColor][jColor] = $(&color, hsv2rgb)(); // Free memory CapyColorDestruct(&color); }

The background generation consists of creating a 2D->3D Bezier

// Create the background void CreateBackground(struct App* const app) { // Create the Bezier to calculate the background uint8_t order = $(RNG, getUInt8Range)(&RANGE_ORDER_BG); CapyBezier bezier = CapyBezierCreate(order, 2, 3); // Loop on the control points loop (iCtrl, bezier.nbCtrls) { // Select a base color and variation uint8_t iColor = $(RNG, getUInt8Range)(&RANGE_IDX_COLOR); uint8_t jColor = $(RNG, getUInt8Range)(&RANGE_IDX_VARIATION(iColor)); // Set the selected color as the control point $(&bezier, setCtrlById)(iCtrl, app->palette[iColor][jColor].rgb); } ... // Refresh the display if necessary REFRESH_DISPLAY; // Free memory CapyBezierDestruct(&bezier); }

and using it to paint the image.

// Loop on the pixels loop (x, app->imgDims.width) loop (y, app->imgDims.height) { // Calculate the normalised position of the pixel in the image to // be used as the Bezier input CapyImgPos pos = {.x=x, .y=y}; double t[2]; loop (i, 2) t[i] = (double)pos.pos[i] / (double)app->imgDims.dims[i]; // Evaluate the color of the pixel with the Bezier CapyColorData color = capyColorRGBAWhite; $(&bezier, eval)(t, color.rgb); // Set the pixel in the image $(&(app->img), setColor)(&pos, &color); }

The foreground is created one stroke at a time.

// Create the foreground void CreateForeground(struct App* const app) { // Get the number of strokes uint64_t nbStroke = $(RNG, getUInt64Range)(&RANGE_NB_STROKE); // Loop on the strokes loop (iStroke, nbStroke) { ... } }

Each stroke receives a random size for the pen and base color from the palette.

// Get the size of the pen double size = $(RNG, getDoubleRange)(&RANGE_SIZE_PEN); // Get the base color uint64_t iColor = $(RNG, getUInt8Range)(&RANGE_IDX_COLOR); // Create the initial Bezier uint8_t order = $(RNG, getUInt8Range)(&RANGE_STROKE_ORDER); CapyBezier bezier = CapyBezierCreate(order, 1, 2); ...

The initial shape of the stroke is created with a 1D->2D Bezier having random control points.

// Loop on the control points loop (iCtrl, bezier.nbCtrls) { // Set the control point to a random position in the image double pos[2]; loop (i, 2) pos[i] = $(RNG, getDoubleRange)(&RANGE_POS(i)); $(&bezier, setCtrlById)(iCtrl, pos); } ... // Free memory CapyBezierDestruct(&bezier);

The stroke is then divided into several substrokes.

// Get the number of substrokes uint64_t nbSubStroke = $(RNG, getUInt8Range)(&RANGE_NB_SUBSTROKE); // Loop on the substrokes loop (iSubStroke, nbSubStroke) { ... }

Each substroke is affected a variation of the base color of the stroke, and a hardness for the pen. The size of the pen and the shape of the stroke are altered as well.

// Get the variation color uint64_t jColor = $(RNG, getUInt8Range)(&RANGE_IDX_VARIATION(iColor)); // Get the hardness of the pen uint8_t hardness = $(RNG, getUInt8Range)(&RANGE_HARDNESS); // Randomise the size size += $(RNG, getDoubleRange)(&RANGE_SIZE_VARIATION); if (size < MIN_SIZE_PEN) size = MIN_SIZE_PEN; if (size > MAX_SIZE_PEN) size = MAX_SIZE_PEN; // Loop on the control points loop (iCtrl, bezier.nbCtrls) { // Randomise the control point values CapyVec const* ctrl = $(&bezier, getCtrlById)(iCtrl); double newPos[2]; loop (i, 2) newPos[i] = ctrl->vals[i] + $(RNG, getDoubleRange)(&RANGE_CTRL_VARIATION); $(&bezier, setCtrlById)(iCtrl, newPos); }

Create a CapyPen and draw the substroke on the image. The color opacity is also altered here for a smoother blending in the image.

// Create the pen CapyPen pen = CapyPenCreate(); pen.hardness = hardness; pen.size = size; pen.color = app->palette[iColor][jColor]; // Randomise the alpha channel pen.color.rgba[3] = $(RNG, getDoubleRange)(&RANGE_ALPHA); // Paint the stroke with the pen $(&pen, drawBezier)(&bezier, &(app->img)); // Free memory CapyPenDestruct(&pen); // Refresh the display if necessary REFRESH_DISPLAY;

Everything put together, it becomes:

/* BezierBg - An abstract image generator based on RNG and Bezier. Copyright (C) 2022 Pascal Baillehache baillehache.pascal@gmail.com https://baillehachepascal.dev This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>. */ #include <LibCapy/capy.h> // Constants #define NB_MAX_BASE_COLOR 4 #define NB_MAX_VARIATION_COLOR 10 #define AMPLITUDE_VARIATION_COLOR 0.1 #define MAX_ORDER_BG 5 #define NB_MAX_STROKE 20 #define MIN_SIZE_PEN (app->imgMinDim / 50) #define MAX_SIZE_PEN (app->imgMaxDim / 25) #define MAX_ORDER_FG ((app->imgMinDim / 100) + 2) #define NB_MIN_SUBSTROKE 5 #define NB_MAX_SUBSTROKE 15 // Shortcuts #define RNG &(app->rng) #define RANGE_NB_MAX_COLOR \ (CapyRangeUInt8){ .min=1, .max=NB_MAX_BASE_COLOR } #define RANGE_NB_MAX_VARIATION \ (CapyRangeUInt8){ .min=1, .max=NB_MAX_VARIATION_COLOR } #define RANGE_VARIATION_COLOR \ (CapyRangeDouble){ \ .min=-0.5*AMPLITUDE_VARIATION_COLOR, \ .max= 0.5*AMPLITUDE_VARIATION_COLOR } #define RANGE_ORDER_BG \ (CapyRangeUInt8){ .min=1, .max=MAX_ORDER_BG } #define RANGE_IDX_COLOR \ (CapyRangeUInt8){ .min=0, .max=app->nbColor-1 } #define RANGE_IDX_VARIATION(i) \ (CapyRangeUInt8){ .min=0, .max=app->nbVariationColor[i]-1 } #define RANGE_NB_STROKE \ (CapyRangeUInt64){ .min=1, .max=NB_MAX_STROKE } #define RANGE_SIZE_PEN \ (CapyRangeDouble){ .min=MIN_SIZE_PEN, .max=MAX_SIZE_PEN } #define RANGE_STROKE_ORDER \ (CapyRangeUInt8){ .min=2, .max=MAX_ORDER_FG } #define RANGE_NB_SUBSTROKE \ (CapyRangeUInt8){ .min=NB_MIN_SUBSTROKE, .max=NB_MAX_SUBSTROKE } #define RANGE_HARDNESS \ (CapyRangeUInt8){ .min=capyPenHardness_9H, .max=capyPenHardness_HB } #define RANGE_SIZE_VARIATION \ (CapyRangeDouble){ .min=-MIN_SIZE_PEN*5, .max=MIN_SIZE_PEN*5 } #define RANGE_CTRL_VARIATION \ (CapyRangeDouble){ .min=-2.0*size, .max=2.0*size } #define RANGE_POS(i) \ (CapyRangeDouble){ .min=-size, .max=app->imgDims.dims[i]+size } #define RANGE_ALPHA \ (CapyRangeDouble){ .min=0.1, .max=1.0 } #define REFRESH_DISPLAY \ if (app->flagDisplay) $(&(app->display), copyImg)(&(app->img)) // App exceptions enum AppExceptions { excInvalidSize = CapyExc_LastID, lastAppException }; // Label for the AppExceptions char* exceptionStr[] = { "Invalid size for the image", }; char const* ExcToStr(int16_t exc) { // If the exception ID is one of AppExceptions, // return the exception's explanation if (exc >= excInvalidSize && exc < lastAppException) return exceptionStr[exc - excInvalidSize]; // Else, the exception ID is not one of AppExceptions, return NULL else return NULL; } // Structure to memorise the appli variables struct App { // Return code at the end of execution int ret; // Appli name char* name; // Parser to process the command line arguments CapyArgParser parser; // Flag for display bool flagDisplay; // Flag for monochrome bool flagGrey; // Display CapyDisplay display; // Random generator CapyRandom rng; // Result image and its dimensions CapyImgDims imgDims; CapyImgDims_t imgMinDim; CapyImgDims_t imgMaxDim; CapyImg img; // Color palette CapyColorData palette[NB_MAX_BASE_COLOR][NB_MAX_VARIATION_COLOR]; uint8_t nbColor; uint8_t nbVariationColor[NB_MAX_BASE_COLOR]; }; // Create the color palette void CreateColorPalette(struct App* const app) { // Set the number of colors and the number of their variations app->nbColor = $(RNG, getUInt8Range)(&RANGE_NB_MAX_COLOR); loop (iColor, app->nbColor) app->nbVariationColor[iColor] = $(RNG, getUInt8Range)(&RANGE_NB_MAX_VARIATION); // Loop on the base colors loop (iColor, app->nbColor) { // Select the base color CapyColorData baseColor = capyColorRGBAWhite; loop (i, 3) baseColor.rgb[i] = $(RNG, getDouble)(); if (app->flagGrey) baseColor.rgb[0] = baseColor.rgb[1] = baseColor.rgb[2]; // Loop on the variations loop (jColor, app->nbVariationColor[iColor]) { // Convert the base color from rgb to hsv CapyColor color = CapyColorCreate(baseColor); CapyColorData hsv = $(&color, rgb2hsv)(); // Create a variation by altering the saturation and value only loop (i, 2) { hsv.hsv[i + 1] += $(RNG, getDoubleRange)(&RANGE_VARIATION_COLOR); if (hsv.hsv[i + 1] < 0.0) hsv.hsv[i + 1] = 0.0; if (hsv.hsv[i + 1] > 1.0) hsv.hsv[i + 1] = 1.0; } // Set the variation in the palette color.vals = hsv; app->palette[iColor][jColor] = $(&color, hsv2rgb)(); // Free memory CapyColorDestruct(&color); } } } // Create the background void CreateBackground(struct App* const app) { // Create the Bezier to calculate the background uint8_t order = $(RNG, getUInt8Range)(&RANGE_ORDER_BG); CapyBezier bezier = CapyBezierCreate(order, 2, 3); // Loop on the control points loop (iCtrl, bezier.nbCtrls) { // Select a base color and variation uint8_t iColor = $(RNG, getUInt8Range)(&RANGE_IDX_COLOR); uint8_t jColor = $(RNG, getUInt8Range)(&RANGE_IDX_VARIATION(iColor)); // Set the selected color as the control point $(&bezier, setCtrlById)(iCtrl, app->palette[iColor][jColor].rgb); } // Loop on the pixels loop (x, app->imgDims.width) loop (y, app->imgDims.height) { // Calculate the normalised position of the pixel in the image to // be used as the Bezier input CapyImgPos pos = {.x=x, .y=y}; double t[2]; loop (i, 2) t[i] = (double)pos.pos[i] / (double)app->imgDims.dims[i]; // Evaluate the color of the pixel with the Bezier CapyColorData color = capyColorRGBAWhite; $(&bezier, eval)(t, color.rgb); // Set the pixel in the image $(&(app->img), setColor)(&pos, &color); } // Refresh the display if necessary REFRESH_DISPLAY; // Free memory CapyBezierDestruct(&bezier); } // Create the foreground void CreateForeground(struct App* const app) { // Get the number of strokes uint64_t nbStroke = $(RNG, getUInt64Range)(&RANGE_NB_STROKE); // Loop on the strokes loop (iStroke, nbStroke) { // Get the size of the pen double size = $(RNG, getDoubleRange)(&RANGE_SIZE_PEN); // Get the base color uint64_t iColor = $(RNG, getUInt8Range)(&RANGE_IDX_COLOR); // Create the initial Bezier uint8_t order = $(RNG, getUInt8Range)(&RANGE_STROKE_ORDER); CapyBezier bezier = CapyBezierCreate(order, 1, 2); // Loop on the control points loop (iCtrl, bezier.nbCtrls) { // Set the control point to a random position in the image double pos[2]; loop (i, 2) pos[i] = $(RNG, getDoubleRange)(&RANGE_POS(i)); $(&bezier, setCtrlById)(iCtrl, pos); } // Get the number of substrokes uint64_t nbSubStroke = $(RNG, getUInt8Range)(&RANGE_NB_SUBSTROKE); // Loop on the substrokes loop (iSubStroke, nbSubStroke) { // Get the variation color uint64_t jColor = $(RNG, getUInt8Range)(&RANGE_IDX_VARIATION(iColor)); // Get the hardness of the pen uint8_t hardness = $(RNG, getUInt8Range)(&RANGE_HARDNESS); // Randomise the size size += $(RNG, getDoubleRange)(&RANGE_SIZE_VARIATION); if (size < MIN_SIZE_PEN) size = MIN_SIZE_PEN; if (size > MAX_SIZE_PEN) size = MAX_SIZE_PEN; // Loop on the control points loop (iCtrl, bezier.nbCtrls) { // Randomise the control point values CapyVec const* ctrl = $(&bezier, getCtrlById)(iCtrl); double newPos[2]; loop (i, 2) newPos[i] = ctrl->vals[i] + $(RNG, getDoubleRange)(&RANGE_CTRL_VARIATION); $(&bezier, setCtrlById)(iCtrl, newPos); } // Create the pen CapyPen pen = CapyPenCreate(); pen.hardness = hardness; pen.size = size; pen.color = app->palette[iColor][jColor]; // Randomise the alpha channel pen.color.rgba[3] = $(RNG, getDoubleRange)(&RANGE_ALPHA); // Paint the stroke with the pen $(&pen, drawBezier)(&bezier, &(app->img)); // Free memory CapyPenDestruct(&pen); // Refresh the display if necessary REFRESH_DISPLAY; } // Free memory CapyBezierDestruct(&bezier); } } // Generate the image void GenerateImg(struct App* const app) { // Update the status in the title bar if (app->flagDisplay) $(&(app->display), setTitle)("generating..."); // Create the image app->img = CapyImgCreate(capyImgMode_rgb, app->imgDims); // Create the color palette CreateColorPalette(app); // Create the background CreateBackground(app); // Create the foreground CreateForeground(app); // Update the status in the title bar if (app->flagDisplay) $(&(app->display), setTitle)(app->name); } // Main function int main( int argc, char** argv) { // Set the conversion function for raised exceptions CapyAddExcToStrFun(ExcToStr); // Instance of the application struct App app; // Initialise the return value app.ret = EXIT_SUCCESS; try { // Definition of the arguments from the command line CapyArg args[] = { {.lbl=argv[0], .nbVal=3, .help="Generate random background images with Bezier curves.\n" "Takes 3 mandatory arguments: <width> <height> <path>\n" "During display of the result, press space to generate " "a new image."}, {.shortLbl="-s", .lbl="--seed", .nbVal=1, .help="Seed for the pseudo-RNG (current time by default)"}, {.shortLbl="-d", .lbl="--display", .nbVal=capyArg_noVal, .help="Display the generated image"}, {.shortLbl="-m", .lbl="--monochrome", .nbVal=capyArg_noVal, .help="Use a greyscale palette"}, }; // Create the argument parser and parse the arguments app.parser = CapyArgParserCreate(argc, argv, args); // Check the requested dimensions app.name = argv[0]; app.imgDims.width = $(&(app.parser), getAsInt)(app.name, 0); app.imgDims.height = $(&(app.parser), getAsInt)(app.name, 1); if (app.imgDims.width <= 0 || app.imgDims.height <= 0) raiseExc(excInvalidSize); // Memorise the appli name and min/max dimensions app.imgMaxDim = (app.imgDims.width > app.imgDims.height ? app.imgDims.width : app.imgDims.height); app.imgMinDim = (app.imgDims.width < app.imgDims.height ? app.imgDims.width : app.imgDims.height); // Initialise the random generator with the given seed or the // current time int64_t seed = time(NULL); if ($(&(app.parser), isSet)("-s")) seed = $(&(app.parser), getAsInt)("-s", 0); app.rng = CapyRandomCreate(seed); // Set the flags app.flagDisplay = $(&(app.parser), isSet)("-d"); app.flagGrey = $(&(app.parser), isSet)("-m"); // If the user requested display during generation if (app.flagDisplay) { // Create the display CapyDisplay d = CapyDisplayCreate(&(app.imgDims), app.name); memcpy(&(app.display), &d, sizeof(CapyDisplay)); $(&(app.display), show)(); // Wait for the display to be ready while ($(&(app.display), isDisplayed)() == false); } // Generate the image GenerateImg(&app); // If the user requested display during generation if (app.flagDisplay) { // Wait until the display has been closed while ($(&(app.display), isDisplayed)()) { // Update the displayed image $(&(app.display), copyImg)(&(app.img)); // Slow down the display as their is nothing in particular to // do but wait CapySleepMs(1000); // Listen to events CapyDisplayKeyEvt evt = $(&(app.display), getKeyPressed)(); // If the user requested to close the display, do it if (evt.keyval == GDK_KEY_q) $(&(app.display), close)(); // If the user requested to generate a new image, do it else if (evt.keyval == GDK_KEY_space) GenerateImg(&app); } } // Save the result image char* pathImg = $(&(app.parser), getAsStr)(app.name, 2); $(&(app.img), saveToPathAsPNG)(pathImg); // Destruct the display if necessary if (app.flagDisplay) CapyDisplayDestruct(&(app.display)); } catchDefault { // Inform the user about the raised exception $(&capyDecoratorRed, fprintf)( stdout, "Sorry, an exception occured. Exiting.\n"); $(&capyDecoratorRed, fprintf)( stdout, "%s\n", CapyExcToStr(CapyGetLastExcId())); app.ret = EXIT_FAILURE; } endCatch; return app.ret; }

Compile with the following Makefile:

CAPY_PARAM=-std=c18 -I./ -Wall -Wextra -Wshadow -Wno-format-truncation -Werror -Wfatal-errors -O3 -ggdb -fopenmp -DPNG_SKIP_SETJMP_CHECK `pkg-config --cflags gtk+-3.0` -D_XOPEN_SOURCE=700 -DCAPY_WITH_GUI=1 CAPY_LINK=-lcapy -lm -fopenmp -lpng `pkg-config --libs gtk+-3.0` bezierbg: main.o Makefile gcc -o bezierbg main.o $(CAPY_LINK) main.o: main.c Makefile gcc $(CAPY_PARAM) -c main.c

Examples of generated image (click to enlarge):