SDL2 doesn't render multiple viewports - c

Question

I'm working through Lazy Foo's SDL2 tutorials and stuck trying to render multiple viewports. The idea is to load a PNG as a texture, create SDL_Rect structs for 3 different viewports (top left, top right, bottom), then copy the texture onto each viewport, and finally render all 3 viewports. My code is only rendering the first viewport.
I've tried changing the order - in every case, whichever viewport is defined first is the only one that renders.
I also tried changing the viewport dimensions, in case overlap was the issue - same problem.
The only question I found about multiple viewports didn't point me in the right direction. But it did start me thinking - my code is written in C, the tutorial in C++. Although I think I'm translating everything correctly (the other lessons work fine), maybe I'm missing something obvious here?
I'm compiling with CFLAGS = -Wall -Wextra -pedantic -std=c99 - no warnings or errors.
Edit: I tried rendering filled rectangles instead of a loaded PNG, but the issue is the same - only the first one renders.
Here's my code:
#include <SDL2/SDL.h>
#include <SDL2/SDL_image.h>
#include <stdio.h>
#define SCREEN_WIDTH 640
#define SCREEN_HEIGHT 480
int init_renderer();
int load_media();
SDL_Texture *load_texture(char *);
void close_renderer();
SDL_Window *g_window = NULL;
SDL_Renderer *g_renderer = NULL;
SDL_Texture *g_texture = NULL;
int main()
{
if (init_renderer() != 1) {
return -1;
}
if (!SDL_SetHint(SDL_HINT_RENDER_SCALE_QUALITY, "1")) {
printf("Warning: Linear texture filtering not enabled!\n");
}
if (load_media() != 1) {
return -1;
}
int quit = 0;
SDL_Event e;
while (quit != 1) {
while (SDL_PollEvent(&e) != 0) {
if (e.type == SDL_QUIT || e.key.keysym.sym == SDLK_q) {
quit = 1;
}
}
SDL_SetRenderDrawColor(g_renderer, 0xff, 0xff, 0xff, 0xff);
SDL_RenderClear(g_renderer);
SDL_Rect top_left_vp;
top_left_vp.x = 0;
top_left_vp.y = 0;
top_left_vp.w = SCREEN_WIDTH / 2;
top_left_vp.h = SCREEN_HEIGHT / 2;
SDL_RenderSetViewport(g_renderer, &top_left_vp);
SDL_RenderCopy(g_renderer, g_texture, NULL, NULL);
SDL_Rect top_right_vp;
top_right_vp.x = SCREEN_WIDTH / 2;
top_right_vp.y = 0;
top_right_vp.w = SCREEN_WIDTH / 2;
top_right_vp.h = SCREEN_HEIGHT / 2;
SDL_RenderSetViewport(g_renderer, &top_right_vp);
SDL_RenderCopy(g_renderer, g_texture, NULL, NULL);
SDL_Rect bottom_vp;
bottom_vp.x = 0;
bottom_vp.y = SCREEN_HEIGHT / 2;
bottom_vp.w = SCREEN_WIDTH;
bottom_vp.h = SCREEN_HEIGHT / 2;
SDL_RenderSetViewport(g_renderer, &bottom_vp);
SDL_RenderCopy(g_renderer, g_texture, NULL, NULL);
SDL_RenderPresent(g_renderer);
}
close_renderer();
return 0;
}
int init_renderer()
{
if (SDL_Init(SDL_INIT_VIDEO) < 0) {
printf("Failed to initialize SDL. Error: %s\n", SDL_GetError());
return 0;
}
g_window = SDL_CreateWindow("SDL Tuts",
SDL_WINDOWPOS_UNDEFINED,
SDL_WINDOWPOS_UNDEFINED,
SCREEN_WIDTH,
SCREEN_HEIGHT,
SDL_WINDOW_SHOWN);
if (g_window == NULL) {
printf("Failed to create window. Error: %s\n", SDL_GetError());
return 0;
}
g_renderer = SDL_CreateRenderer(g_window, -1, SDL_RENDERER_ACCELERATED);
if (g_renderer == NULL) {
printf("Failed to create renderer. Error: %s\n", SDL_GetError());
return 0;
}
SDL_SetRenderDrawColor(g_renderer, 0x29, 0xAB, 0x87, 0xFF);
int img_flags = IMG_INIT_PNG;
if (!(IMG_Init(img_flags) & img_flags)) {
printf("Failed to initialize SDL Image. SDL_Image Error: %s\n", IMG_GetError());
return 0;
}
return 1;
}
int load_media()
{
g_texture = load_texture("assets/texture.png");
if (g_texture == NULL) {
return 0;
}
return 1;
}
SDL_Texture *load_texture(char *path)
{
SDL_Texture *new_texture = NULL;
SDL_Surface *loaded_surface = IMG_Load(path);
if (loaded_surface == NULL) {
printf("Failed to load image. SDL_Image Error: %s\n", IMG_GetError());
} else {
new_texture = SDL_CreateTextureFromSurface(g_renderer, loaded_surface);
if (new_texture == NULL) {
printf("Failed to create texture from %s. Error: %s\n", path, SDL_GetError());
}
SDL_FreeSurface(loaded_surface);
}
return new_texture;
}
void close_renderer()
{
SDL_DestroyTexture(g_texture);
g_texture = NULL;
SDL_DestroyRenderer(g_renderer);
SDL_DestroyWindow(g_window);
g_renderer = NULL;
g_window = NULL;
IMG_Quit();
SDL_Quit();
}

Answer 1

To check for more errors, you should see what the calls to SDL_RenderSetViewPort are returning. According to the docs, it returns an int, which is 0 on success or a negative int if there's an error. It's entirely possible that something deeper in SDL is having a fit.
Additional pro tips: you can define the SDL_Rect structs outside of your while loop to save a miniscule margin of processing power. And to spare yourself some typing, you can initialize a SDL_Rect using a list constructor instead of manually punching each property. E.G.:
SDL_Rect top_left_vp;
top_left_vp.x = 0;
top_left_vp.y = 0;
top_left_vp.w = SCREEN_WIDTH / 2;
top_left_vp.h = SCREEN_HEIGHT / 2;
is more simply
SDL_Rect top_left_vp = {
0,
0,
SCREEN_WIDTH / 2,
SCREEN_HEIGHT / 2
};