How can I preserve alpha values when blitting? I want to blit multiple black squares with various alpha values onto a surface and then blit that surface onto the screen. Everything I try just blits a solid opaque black surface.
Edit:
What I want is this:
What I'm getting is this:
The code
#include <SDL.h>
void putPixel(SDL_Surface *surface, int x, int y, Uint32 pixel){
Uint32 *pixels = (Uint32*)surface->pixels;
pixels[(y * surface->w) + x] = pixel;
}
void FillAlpha(SDL_Surface* Surface){
Uint32 Pixel;
Uint8 RGBA[4] = {0, 0, 0, 100};
Pixel = RGBA[3]<<24 | RGBA[2]<<16 | RGBA[1]<<8 | RGBA[0];
for(int x=0; x<32; x++){
for(int y=0; y<32; y++){
putPixel(Surface, x, y, Pixel);
}
}
RGBA[3] = 150;
Pixel = RGBA[3]<<24 | RGBA[2]<<16 | RGBA[1]<<8 | RGBA[0];
for(int x=32; x<64; x++){
for(int y=0; y<32; y++){
putPixel(Surface, x, y, Pixel);
}
}
}
int main(int argc, char* args[])
{
SDL_Window* Window = NULL;
SDL_Surface* Screen = NULL;
SDL_Surface* Alpha = NULL;
SDL_Event Event;
bool Quit = false;
Window = SDL_CreateWindow("Alpha test", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 128, 128, SDL_WINDOW_SHOWN);
if(Window == NULL) return 1;
Screen = SDL_GetWindowSurface(Window);
if(Screen == NULL) return 2;
Alpha = SDL_CreateRGBSurface(NULL, 64, 32, 32,
Screen->format->Rmask, Screen->format->Gmask,
Screen->format->Bmask, Screen->format->Amask);
if(Alpha == NULL) return 3;
SDL_SetSurfaceBlendMode(Alpha, SDL_BLENDMODE_BLEND);
FillAlpha(Alpha);
while(!Quit){
while(SDL_PollEvent(&Event)){
if(Event.type == SDL_KEYDOWN){
if(Event.key.keysym.sym == SDLK_ESCAPE){
Quit = true;
}
}else if(Event.type == SDL_QUIT){
Quit = true;
}
}
SDL_FillRect(Screen, NULL, SDL_MapRGB(Screen->format, 255, 255, 255));
SDL_BlitSurface(Alpha, NULL, Screen, NULL);
SDL_UpdateWindowSurface(Window);
}
SDL_Quit();
return 0;
}
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I'm trying to make a game in C++ with SDL2, and I can't even get a texture displaying. SDL_GetError() returns nothing.
I'm on a windows 10 pro using Visual Studio.
Here are my 3 files:
main.cpp
#include "Classes.h"
int MouseX = 0;
int MouseY = 0;
int PlayerX = 0;
int PlayerY = 0;
SDL_Renderer* renderer;
Tile tile = Tile({10, 10, TileTypes::Tile_Grass}, renderer);
EventReturns HandleEvent(SDL_Event* event) {
switch (event->type) {
case SDL_QUIT:
return EventReturns::Event_QUIT;
case SDL_KEYDOWN:
switch (event->key.keysym.sym) {
case SDLK_ESCAPE:
return EventReturns::Event_TryQuit;
default:
return EventReturns::Event_None;
}
default:
return EventReturns::Event_None;
}
}
int mainLoop(EventReturns eventReturn) {
SDL_GetMouseState(&MouseX, &MouseY);
if (eventReturn == EventReturns::Event_QUIT || eventReturn == EventReturns::Event_TryQuit) {
return 1;
}
return 0;
}
void render() {
SDL_SetRenderDrawColor(renderer, 100, 200, 200, 255);
SDL_RenderClear(renderer);
SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
tile.SetPos(0, 0);
if (tile.Draw(renderer) != 0) {
SDL_ShowSimpleMessageBox(0, "ERROR", "ERROR: Rect in tile has 0x0 size, Please close this with the task manager", NULL);
}
SDL_RenderPresent(renderer);
}
int main(int argc, char* argv[]) {
SDL_Window* window = SDL_CreateWindow("Game", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 2880, 1600, SDL_WINDOW_SHOWN);
renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);
bool running = true;
EventReturns eventReturn = EventReturns::Event_None;
SDL_Event event;
int quit = 0;
while (running) {
while (SDL_PollEvent(&event)) {
eventReturn = HandleEvent(&event);
}
quit = mainLoop(eventReturn);
render();
if (quit == 1) {
running = false;
}
}
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
return 0;
}
Classes.h
#pragma once
#include <SDL.h>
#include <SDL_image.h>
#include <iostream>
#define SpriteSizeMult 1
enum class EventReturns {
Event_QUIT,
Event_None,
Event_TryQuit
};
enum class TileTypes {
Tile_Grass
};
struct TileStruct {
int x;
int y;
TileTypes type;
};
class Tile {
public:
Tile(int x, int y, char* TexturePath, SDL_Renderer* renderer);
Tile(TileStruct structure, SDL_Renderer* renderer);
Tile();
int Draw(SDL_Renderer* renderer);
void SetPos(int x, int y);
private:
int x = 0;
int y = 0;
int TextureWidth = 0;
int TextureHeight = 0;
SDL_Texture* texture;
SDL_Rect rect;
};
SDL_Point getsize(SDL_Texture* texture);
Classes.cpp
#include "Classes.h"
SDL_Point getsize(SDL_Texture* texture) {
SDL_Point size;
SDL_QueryTexture(texture, NULL, NULL, &size.x, &size.y);
return size;
}
Tile::Tile(int x, int y, char* TexturePath, SDL_Renderer* renderer)
{
this->x = x;
this->y = y;
this->texture = SDL_CreateTextureFromSurface(renderer, IMG_Load(TexturePath));
if (this->texture == nullptr) {
this->texture = SDL_CreateTextureFromSurface(renderer, IMG_Load("Assets/MissingTexture.png"));
std::cout << IMG_GetError();
}
SDL_Point point = getsize(this->texture);
this->TextureHeight = point.y;
this->TextureWidth = point.x;
this->rect = {this->x - ((this->TextureWidth * SpriteSizeMult) / 2), this->y - ((this->TextureHeight * SpriteSizeMult) / 2), this->TextureWidth * SpriteSizeMult, this->TextureHeight * SpriteSizeMult};
}
Tile::Tile(TileStruct structure, SDL_Renderer* renderer)
{
this->x = structure.x;
this->y = structure.y;
switch (structure.type) {
case TileTypes::Tile_Grass:
this->texture = SDL_CreateTextureFromSurface(renderer, IMG_Load("Assets/Tiles/Grass.png"));
default:
this->texture = SDL_CreateTextureFromSurface(renderer, IMG_Load("Assets/MissingTexture.png"));
}
if (this->texture == NULL) {
this->texture = SDL_CreateTextureFromSurface(renderer, IMG_Load("Assets/MissingTexture.png"));
if (this->texture == NULL) {
SDL_ShowSimpleMessageBox(0, "ERROR", "Failed to load texture", NULL);
SDL_ShowSimpleMessageBox(0, "ERROR", IMG_GetError(), NULL);
}
}
SDL_Point point = getsize(this->texture);
this->TextureHeight = point.y;
this->TextureWidth = point.x;
this->rect = { this->x - ((this->TextureWidth * SpriteSizeMult) / 2), this->y - ((this->TextureHeight * SpriteSizeMult) / 2), this->TextureWidth * SpriteSizeMult, this->TextureHeight * SpriteSizeMult };
}
Tile::Tile()
{
}
int Tile::Draw(SDL_Renderer* renderer)
{
if (rect.w == 0 || rect.h == 0) {
return -1;
}
this->rect.x = 0;
this->rect.y = 0;
SDL_RenderCopy(renderer, this->texture, NULL, &rect);
return 0;
}
void Tile::SetPos(int x, int y)
{
this->x = x;
this->y = y;
}
I'm sorry for the sheer amount of code that is, but I'd really appreciate the help. If there's any more info I need to put here, just let me know.
I'm fully aware that I should make a Minimal Reproducible Example, but as far as I'm aware, all the code listed here is necessary.
Finally, in case I've been unclear, when running the code the Missing Texture image that should appear isn't showing up.
I can't see SDL_INIT function in your code.
You should add this in the beginning of your main function.
if (SDL_Init(SDL_INIT_EVERYTHING) != 0)
return 1;
You are initialising tile before creating a renderer so the constructor is trying to create a texture without a renderer.
SDL_Renderer* renderer;
Tile tile = Tile({10, 10, TileTypes::Tile_Grass}, renderer);
You should do something like this
#include "Classes.h"
int MouseX = 0;
int MouseY = 0;
int PlayerX = 0;
int PlayerY = 0;
SDL_Renderer* renderer;
EventReturns HandleEvent(SDL_Event* event) {
switch (event->type) {
case SDL_QUIT:
return EventReturns::Event_QUIT;
case SDL_KEYDOWN:
switch (event->key.keysym.sym) {
case SDLK_ESCAPE:
return EventReturns::Event_TryQuit;
default:
return EventReturns::Event_None;
}
default:
return EventReturns::Event_None;
}
}
int mainLoop(EventReturns eventReturn) {
SDL_GetMouseState(&MouseX, &MouseY);
if (eventReturn == EventReturns::Event_QUIT || eventReturn == EventReturns::Event_TryQuit) {
return 1;
}
return 0;
}
void render(Tile tile) {
SDL_SetRenderDrawColor(renderer, 100, 200, 200, 255);
SDL_RenderClear(renderer);
SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
tile.SetPos(0, 0);
if (tile.Draw(renderer) != 0) {
SDL_ShowSimpleMessageBox(0, "ERROR", "ERROR: Rect in tile has 0x0 size, Please close this with the task manager", NULL);
}
SDL_RenderPresent(renderer);
}
int main(int argc, char* argv[]) {
if (SDL_Init(SDL_INIT_EVERYTHING) != 0)
return 1;
SDL_Window* window = SDL_CreateWindow("Game", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 2880, 1600, SDL_WINDOW_SHOWN);
renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);
Tile tile = Tile({ 10, 10, TileTypes::Tile_Grass }, renderer);
bool running = true;
EventReturns eventReturn = EventReturns::Event_None;
SDL_Event event;
int quit = 0;
while (running) {
while (SDL_PollEvent(&event)) {
eventReturn = HandleEvent(&event);
}
quit = mainLoop(eventReturn);
render(tile);
if (quit == 1) {
running = false;
}
}
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
return 0;
}
Im following this (https://www.udemy.com/course/free-learn-c-tutorial-beginners/learn/lecture/1838486#announcements ) tutorial and im stuck.
It seem that windows throws that exception and it cant be handled.
I think I try write something to some wrong place but cant see it.
Heres the line that causes the problem.
m_buffer[(y * SCREEN_WIDTH) + x] = color;
And here is everything else
//====================================main.cpp=======================================
#include<iostream>
#include "Screen.h"
#include<SDL.h>
using namespace std;
int main(int argc, char* argv[]) {
Screen screen;
if (!screen.init()) {
cout << "Error initialising SDL." << endl;
}
while (true) {
// update particles
// draw particles
for (int y = 0; y < Screen::SCREEN_HEIGHT; y++) {
for (int x = 0; x < Screen::SCREEN_WIDTH; x++ ){
screen.setPixel(x, y, 128, 0, 255);
}
}
//Draw the screen
screen.update();
// see for messages/events
if (!screen.processEvents()) {
break;
}
}
screen.close();
return 0;
}
//==========================================================================================
screen.h
#ifndef SCREEN_H_
#define SCREEN_H_
#include<SDL.h>
#include<iostream>
class Screen
{
public:
const static int SCREEN_WIDTH = 800;
const static int SCREEN_HEIGHT = 600;
private:
SDL_Window* m_window;
SDL_Renderer* m_renderer;
SDL_Texture* m_texture;
Uint32* m_buffer;
public:
Screen();
bool init();
void update();
void setPixel(int x, int y, Uint8 red, Uint8 green, Uint8 blue);
bool processEvents();
void close();
};
#endif // !SCREEN_H_
//=======================screen.cpp======================================================
#include "Screen.h"
Screen::Screen() : m_window(NULL), m_renderer(NULL), m_texture(NULL), m_buffer(NULL)
{
}
bool Screen::init() {
if (SDL_Init(SDL_INIT_VIDEO) < 0) {
return false;
}
m_window = SDL_CreateWindow("Particle Fire Explosion",
SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN); //-----------------SDL_WINDOW_HIDDEN SDL_WINDOW_SHOWN
if (m_window == 0) {
SDL_Quit();
return false;
}
m_renderer = SDL_CreateRenderer(m_window, -1, SDL_RENDERER_PRESENTVSYNC);
m_texture = SDL_CreateTexture(m_renderer,
SDL_PIXELFORMAT_RGBA8888, SDL_TEXTUREACCESS_STATIC, SCREEN_WIDTH, SCREEN_HEIGHT);
if (m_renderer == NULL) {
SDL_DestroyWindow(m_window);
SDL_Quit();
return false;
}
if (m_texture == NULL) {
SDL_DestroyWindow(m_window);
SDL_DestroyRenderer(m_renderer);
SDL_Quit();
return false;
}
Uint32* buffer = new Uint32[SCREEN_WIDTH * SCREEN_HEIGHT];
memset(buffer, 0xFF, SCREEN_WIDTH * SCREEN_HEIGHT * sizeof(Uint32));
return true;
}
bool Screen::processEvents() {
SDL_Event event;
while (SDL_PollEvent(&event)) {
if (event.type == SDL_QUIT)
{
return false;
}
}
return true;
}
void Screen::setPixel(int x, int y, Uint8 red, Uint8 green, Uint8 blue) {
Uint32 color = 0;
color += red;
color <<= 8;
color += green;
color <<= 8;
color += blue;
color <<= 8;
color += 0xFF;
m_buffer[(y * SCREEN_WIDTH) + x] = color;
}
void Screen::update() {
SDL_UpdateTexture(m_texture, NULL, m_buffer, SCREEN_WIDTH * sizeof(Uint32));
SDL_RenderClear(m_renderer);
SDL_RenderCopy(m_renderer, m_texture, NULL, NULL);
SDL_RenderPresent(m_renderer);
}
void Screen::close() {
delete[] m_buffer;
SDL_DestroyRenderer(m_renderer);
SDL_DestroyTexture(m_texture);
SDL_DestroyWindow(m_window);
SDL_Quit();
}
//==========================================================================================
Maybe someone can see what is the broblem?
Your Screen::init() method never sets m_buffer, so when setPixel() tries to dereference it, it is dereferencing a NULL pointer, which invokes undefined behavior.
this line is wrong
Uint32* buffer = new Uint32[SCREEN_WIDTH * SCREEN_HEIGHT];
you mean
m_buffer = new Uint32[SCREEN_WIDTH * SCREEN_HEIGHT];
I'm making a little game as a small project but I can't get an if statement to do anything. If I make it !statement it works though. I run this if statement to find which cube on the "grid" (An array or cubes I render in a for loop I didn't show) the mouse clicked on. I use C++ and SDL2 on a Mac. This is my code:
#include <iostream>
#include <SDL2/SDL.h>
void RenderRects(SDL_Renderer *renderer);
void ToggleRect(int MouseX, int MouseY);
struct Grid
{
bool IsActive;
SDL_Rect Rect;
};
Grid grid[228960];
int main()
{
bool IsRunning = true;
bool IsRunningSim;
SDL_Init(SDL_INIT_EVERYTHING);
SDL_Window *window = SDL_CreateWindow("My Game", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 1000, 780, SDL_WINDOW_SHOWN | SDL_WINDOW_RESIZABLE);
SDL_Renderer *renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);
int h, w;
SDL_MaximizeWindow(window);
SDL_GetRendererOutputSize(renderer, &w, &h);
while (IsRunning)
{
// std::cout << w << std::endl;
// std::cout << h << std::endl;
SDL_Event ev;
while (SDL_PollEvent(&ev))
{
if (ev.type == SDL_QUIT)
{
IsRunning = false;
}
if (ev.type == SDL_MOUSEBUTTONDOWN)
{
int x, y;
SDL_GetMouseState(&x, &y);
ToggleRect(x, y);
}
}
SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
SDL_RenderClear(renderer);
//rendering
RenderRects(renderer);
SDL_RenderPresent(renderer);
}
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
return 0;
}
void RenderRects(SDL_Renderer *renderer)
{
for (int i = 0; i < 1440; i += 10)
{
for (int j = 0; j < 795; j += 10)
{
SDL_Rect Rect = {i, j, 10, 10};
grid[i].Rect = Rect;
SDL_SetRenderDrawColor(renderer, 100, 100, 100, 225);
SDL_RenderDrawRect(renderer, &grid[i].Rect);
}
}
}
void ToggleRect(int MouseX, int MouseY)
{
SDL_Point MousePos;
MousePos.x = MouseX;
MousePos.y = MouseY;
for (int i = 0; i < 228961; i++)
{
if (SDL_PointInRect(&MousePos, &grid[i].Rect)) //This is the if that doesn't work.
{
std::cout << i << std::endl;
}
}
}
I have fixed this. I had to change my method of drawing since it was drawing over the rect and then showing after I changed its color. There was also an issue with generating the Rects that was probably effect it.
This is basically my code here, very simple just to load an image to display. But the first thing I open a window surface, the surface has characters like 'X','S' out of nowhere:
int main( int argc, char* args[] )
{
SDL_Init( SDL_INIT_VIDEO );
SDL_Surface* screen = SDL_SetVideoMode( WINDOW_WIDTH, WINDOW_HEIGHT, 0,
SDL_HWSURFACE | SDL_DOUBLEBUF );
SDL_WM_SetCaption( WINDOW_TITLE, 0 );
SDL_Surface* bitmap = SDL_LoadBMP("bat.bmp");
// Part of the bitmap that we want to draw
SDL_Rect source;
source.x = 24;
source.y = 63;
source.w = 65;
source.h = 44;
// Part of the screen we want to draw the sprite to
SDL_Rect destination;
destination.x = 100;
destination.y = 100;
destination.w = 65;
destination.h = 44;
SDL_Event event;
bool gameRunning = true;
int i=1000;
while (i)
{
if (SDL_PollEvent(&event))
{
if (event.type == SDL_QUIT)
{
gameRunning = false;
}
}
SDL_BlitSurface(bitmap, &source, screen, &destination);
SDL_Flip(screen);
i--;
}
SDL_FreeSurface(bitmap);
SDL_Quit();
return 0;
}
I have an image which I want to be moveable. My problem is that the image isn't really moving, it's just dublicated and a new image loads on the new place while the old position still contain the image.
void draw_surface(int srcX, int srcY, int dstX, int dstY, int width, int height, SDL_Surface *source, SDL_Surface *destination)
{
SDL_Rect src;
src.x = srcX;
src.y = srcY;
src.w = width;
src.h = height;
SDL_Rect dst;
dst.x = dstX;
dst.y = dstY;
dst.w = width;
dst.h = height;
SDL_BlitSurface(source, &src, destination, &dst);
}
in the main function:
while (gameRunning)
{
if (SDL_PollEvent(&event))
{
if (event.type == SDL_QUIT)
{
gameRunning = false;
}
if (event.type == SDL_KEYDOWN)
{
if (event.key.keysym.sym == SDLK_DOWN)
{
dstY += 10; //new position
}
}
//apply
apply_surface(0, 10, background, screen);
draw_surface(srcX, srcY, dstX, dstY, width, heigth, background, screen);
}
//update screen
SDL_Flip(screen);
}
What's wrong with this code?
You should use a while loop to poll for events
Moving the drawing outside of the event loop block is a good idea
You need to clear your screen before drawing to it or else the old back buffer data will still be on it
Uint32 black = SDL_MapRGB(screen->format, 0, 0, 0);
while (gameRunning) {
while (SDL_PollEvent(&event)) {
if (event.type == SDL_QUIT) {
gameRunning = false;
}
if (event.type == SDL_KEYDOWN) {
if (event.key.keysym.sym == SDLK_DOWN) {
dstY += 10; //new position
}
}
}
// Clear screen
SDL_FillRect(screen, NULL, black);
//apply
apply_surface(0, 10, background, screen);
draw_surface(srcX, srcY, dstX, dstY, width, heigth, background, screen);
//update screen
SDL_Flip(screen);
}