SDL 2 Lessons: Lesson 6 - Primitives

Hello everyone, this is the sixth lesson on SDL 2 and it came out small, but it is worth going. All lessons are here .

In this lesson we will draw drawing of primitives. Let's get started and welcome to the lesson

Primitives

First, let’s see what a primitive is. A graphic primitive is the simplest geometric object displayed on the display screen: a point, a line segment, a rectangle, an arc, a circle, etc. In SDL 2, we can only draw points, rectangles, and lines.

Let's get down to code

#include 
#include 
using namespace std;
int SCREEN_WIDTH = 640;
int SCREEN_HEIGHT = 480;
SDL_Window *win = NULL;
SDL_Renderer *ren = NULL;

I will not describe the declaration of variables, let's move on.

bool init() {
    bool ok = true;
    if (SDL_Init(SDL_INIT_VIDEO) != 0) {
        cout << "Can't init SDL: " << SDL_GetError() << endl;
    }
    win = SDL_CreateWindow("Примитивы", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
    if (win == NULL) {
        cout << "Can't create window: " << SDL_GetError() << endl;
        ok = false;
    }
    ren = SDL_CreateRenderer(win, -1, SDL_RENDERER_ACCELERATED);
    if (ren == NULL) {
        cout << "Can't create renderer: " << SDL_GetError() << endl;
        ok = false;
    }
    return ok;
}

In Init, initialize SDL 2, create a window and render here, too, do not linger. I do not write the Load

function , since we do not need to load anything. In the Quit function, we simply remove the window, render and uninitialize SDL 2.

void quit() {
    SDL_DestroyWindow(win);
    win = NULL;
    SDL_DestroyRenderer(ren);
    ren = NULL;
    SDL_Quit;
}

I’ll skip the call to the Init function and move on to the most interesting part. In order to draw a rectangle, we need to create an object of type SDL_Rect . Its coordinates and dimensions are needed for drawing.

A little about SDL_Rect : this data type is an array of 4 numbers: x , y , w and h - in that order. That is, this code: SDL_Rect rect = {1, 1, 1, 1}; - completely correct.

This completes the theory about SDL_Rect, let 's start writing code.

    SDL_SetRenderDrawColor(ren, 0x00, 0x00, 0x00, 0x00);
    SDL_RenderClear(ren);
    SDL_SetRenderDrawColor(ren, 0xFF, 0xFF, 0xFF, 0xFF);
    SDL_Rect rect1 = {10, 10, 50, 50};
    SDL_RenderFillRect(ren, &rect1);

Here we were told the render to paint in black and fill them with the whole window. After that they said to paint in white. Next, we created a rectangle with coordinates (10; 10) and dimensions 50x50. The SDL_RenderFillRect function draws a rectangle.

Drawing only the outline of the rectangle is not much different.

    SDL_Rect rect2 = {70, 10, 50, 50};
    SDL_RenderDrawRect(ren, &rect2);

We created a rectangle and called the SDL_RenderDrawRect function . She only draws the outline of the rectangle on the screen.

The next step is to draw a line.

    SDL_RenderDrawLine(ren, 10, 70, 640 - 10, 70);

A rectangle is not needed to draw a line. The SDL_RenderDrawLine function accepts render values ​​and four coordinates. These are the coordinates of the start point and end point. I decided to draw a horizontal line indented from the edges by 10 pixels.

Drawing points is almost no different from drawing lines. We call the SDL_RenderDrawPoint function and pass in the render and the coordinates of the point. But just to draw a point is not interesting, let's write for better , in which through 3 pixels we will draw points.

    for (int i = 10; i <= 640-10; i +=4 ) {
        SDL_RenderDrawPoint(ren, i, 90);
    }

We got a horizontal dotted line of dots.

On this drawing has stopped. It remains only to update the screen, set the pause time, exit and return 0 .

    SDL_RenderPresent(ren);
    SDL_Delay(5000);
    quit();
    return 0;
}

This concludes our lesson, here is the complete code:

#include 
#include 
using namespace std;
int SCREEN_WIDTH = 640;
int SCREEN_HEIGHT = 480;
SDL_Window *win = NULL;
SDL_Renderer *ren = NULL;
bool init() {
    bool ok = true;
    if (SDL_Init(SDL_INIT_VIDEO) != 0) {
        cout << "Can't init SDL: " << SDL_GetError() << endl;
    }
    win = SDL_CreateWindow("Примитивы", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
    if (win == NULL) {
        cout << "Can't create window: " << SDL_GetError() << endl;
        ok = false;
    }
    ren = SDL_CreateRenderer(win, -1, SDL_RENDERER_ACCELERATED);
    if (ren == NULL) {
        cout << "Can't create renderer: " << SDL_GetError() << endl;
        ok = false;
    }
    return ok;
}
void quit() {
    SDL_DestroyWindow(win);
    win = NULL;
    SDL_DestroyRenderer(ren);
    ren = NULL;
    SDL_Quit;
}
int main (int arhc, char ** argv) {
    if (!init()) {
        quit();
        system("pause");
        return 1;
    }
    SDL_SetRenderDrawColor(ren, 0x00, 0x00, 0x00, 0x00);
    SDL_RenderClear(ren);
    SDL_SetRenderDrawColor(ren, 0xFF, 0xFF, 0xFF, 0xFF);
    SDL_Rect rect1 = {10, 10, 50, 50};
    SDL_RenderFillRect(ren, &rect1);
    SDL_Rect rect2 = {70, 10, 50, 50};
    SDL_RenderDrawRect(ren, &rect2);
    SDL_RenderDrawLine(ren, 10, 70, 640 - 10, 70);
    for (int i = 10; i <= 640-10; i +=4 ) {
        SDL_RenderDrawPoint(ren, i, 90);
    }
    SDL_RenderPresent(ren);
    SDL_Delay(5000);
    quit();
    return 0;
}

And I say goodbye to you, bye everyone!

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