Hey so I'm relatively new to the SDL library and just trying to get to grips with it.
I found a C++ conversion for Minecraft4k but it was based on SDL1.x so I'm trying to convert it to SDL2.0
At present the build is successful, but when it gets to;
plot(x, y, rgbmul(col, fxmul(br, ddist)));
It throws a read access violation exception:
screen was nullptr
This is my code;
// C++ port of Minecraft 4k JS (http://jsdo.it/notch/dB1E)
// By The8BitPimp
// See: the8bitpimp.wordpress.com
#include <SDL.h>
#include <math.h>
#include <windows.h>
#include <tchar.h>
#include "plot.h"
#include "llist.h"
const int w = 320;
const int h = 240;
SDL_Surface *screen = nullptr;
const float math_pi = 3.14159265359f;
static inline float math_sin(float x) {
return sinf(x);
}
static inline float math_cos(float x) {
return cosf(x);
}
// the texture map
int texmap[16 * 16 * 16 * 3];
// the voxel map
char map[64 * 64 * 64];
static inline int random(int max) {
return (rand() ^ (rand() << 16)) % max;
}
static inline void plot(int x, int y, int c) {
int *p = (int*)screen->pixels;
p[y * w + x] = c;
}
static void makeTextures(void) {
// each texture
for (int j = 0; j<16; j++) {
int k = 255 - random(96);
// each pixel in the texture
for (int m = 0; m<16 * 3; m++)
for (int n = 0; n<16; n++) {
int i1 = 0x966C4A;
int i2 = 0;
int i3 = 0;
if (j == 4)
i1 = 0x7F7F7F;
if ((j != 4) || (random(3) == 0))
k = 255 - random(96);
if (j == 1)
{
if (m < (((n * n * 3 + n * 81) >> 2) & 0x3) + 18)
i1 = 0x6AAA40;
else if (m < (((n * n * 3 + n * 81) >> 2) & 0x3) + 19)
k = k * 2 / 3;
}
if (j == 7)
{
i1 = 0x675231;
if ((n > 0) && (n < 15) && (((m > 0) && (m < 15)) || ((m > 32) && (m < 47))))
{
i1 = 0xBC9862;
i2 = n - 7;
i3 = (m & 0xF) - 7;
if (i2 < 0)
i2 = 1 - i2;
if (i3 < 0)
i3 = 1 - i3;
if (i3 > i2)
i2 = i3;
k = 196 - random(32) + i2 % 3 * 32;
}
else if (random(2) == 0)
k = k * (150 - (n & 0x1) * 100) / 100;
}
if (j == 5)
{
i1 = 0xB53A15;
if (((n + m / 4 * 4) % 8 == 0) || (m % 4 == 0))
i1 = 0xBCAFA5;
}
i2 = k;
if (m >= 32)
i2 /= 2;
if (j == 8)
{
i1 = 5298487;
if (random(2) == 0)
{
i1 = 0;
i2 = 255;
}
}
// fixed point colour multiply between i1 and i2
i3 =
((((i1 >> 16) & 0xFF) * i2 / 255) << 16) |
((((i1 >> 8) & 0xFF) * i2 / 255) << 8) |
((i1 & 0xFF) * i2 / 255);
// pack the colour away
texmap[n + m * 16 + j * 256 * 3] = i3;
}
}
}
static void makeMap(void) {
// add random blocks to the map
for (int x = 0; x < 64; x++) {
for (int y = 0; y < 64; y++) {
for (int z = 0; z < 64; z++) {
int i = (z << 12) | (y << 6) | x;
float yd = (y - 32.5) * 0.4;
float zd = (z - 32.5) * 0.4;
map[i] = random(16);
float th = random(256) / 256.0f;
if (th > sqrtf(sqrtf(yd * yd + zd * zd)) - 0.8f)
map[i] = 0;
}
}
}
}
static void init(void) {
makeTextures();
makeMap();
}
// fixed point byte byte multiply
static inline int fxmul(int a, int b) {
return (a*b) >> 8;
}
// fixed point 8bit packed colour multiply
static inline int rgbmul(int a, int b) {
int _r = (((a >> 16) & 0xff) * b) >> 8;
int _g = (((a >> 8) & 0xff) * b) >> 8;
int _b = (((a)& 0xff) * b) >> 8;
return (_r << 16) | (_g << 8) | _b;
}
static void render(void) {
float now = (float)(SDL_GetTicks() % 10000) / 10000.f;
float xRot = math_sin(now * math_pi * 2) * 0.4 + math_pi / 2;
float yRot = math_cos(now * math_pi * 2) * 0.4;
float yCos = math_cos(yRot);
float ySin = math_sin(yRot);
float xCos = math_cos(xRot);
float xSin = math_sin(xRot);
float ox = 32.5 + now * 64.0;
float oy = 32.5;
float oz = 32.5;
// for each column
for (int x = 0; x < w; x++) {
// get the x axis delta
float ___xd = ((float)x - (float)w / 2.f) / (float)h;
// for each row
for (int y = 0; y < h; y++) {
// get the y axis delta
float __yd = ((float)y - (float)h / 2.f) / (float)h;
float __zd = 1;
float ___zd = __zd * yCos + __yd * ySin;
float _yd = __yd * yCos - __zd * ySin;
float _xd = ___xd * xCos + ___zd * xSin;
float _zd = ___zd * xCos - ___xd * xSin;
int col = 0;
int br = 255;
float ddist = 0;
float closest = 32.f;
// for each principle axis x,y,z
for (int d = 0; d < 3; d++) {
float dimLength = _xd;
if (d == 1)
dimLength = _yd;
if (d == 2)
dimLength = _zd;
float ll = 1.0f / (dimLength < 0.f ? -dimLength : dimLength);
float xd = (_xd)* ll;
float yd = (_yd)* ll;
float zd = (_zd)* ll;
float initial = ox - floor(ox);
if (d == 1) initial = oy - floor(oy);
if (d == 2) initial = oz - floor(oz);
if (dimLength > 0) initial = 1 - initial;
float dist = ll * initial;
float xp = ox + xd * initial;
float yp = oy + yd * initial;
float zp = oz + zd * initial;
if (dimLength < 0) {
if (d == 0) xp--;
if (d == 1) yp--;
if (d == 2) zp--;
}
// while we are concidering a ray that is still closer then the best so far
while (dist < closest) {
// quantize to the map grid
int tex = map[(((int)zp & 63) << 12) | (((int)yp & 63) << 6) | ((int)xp & 63)];
// if this voxel has a texture applied
if (tex > 0) {
// find the uv coordinates of the intersection point
int u = ((int)((xp + zp) * 16.f)) & 15;
int v = ((int)(yp * 16.f) & 15) + 16;
// fix uvs for alternate directions?
if (d == 1) {
u = ((int)(xp * 16.f)) & 15;
v = (((int)(zp * 16.f)) & 15);
if (yd < 0)
v += 32;
}
// find the colour at the intersection point
int cc = texmap[u + v * 16 + tex * 256 * 3];
// if the colour is not transparent
if (cc > 0) {
col = cc;
ddist = 255 - ((dist / 32 * 255));
br = 255 * (255 - ((d + 2) % 3) * 50) / 255;
// we now have the closest hit point (also terminates this ray)
closest = dist;
}
}
// advance the ray
xp += xd;
yp += yd;
zp += zd;
dist += ll;
}
}
plot(x, y, rgbmul(col, fxmul(br, ddist)));
}
}
}
int main(int argc, char *argv[]) {
SDL_Init(SDL_INIT_EVERYTHING);
SDL_Window *screen;
screen = SDL_CreateWindow(
"Minecraft4k", // window title
SDL_WINDOWPOS_CENTERED, // initial x position
SDL_WINDOWPOS_CENTERED, // initial y position
320, // width, in pixels
240, // height, in pixels
SDL_WINDOW_OPENGL // flags - see below
);
SDL_Renderer* renderer;
renderer = SDL_CreateRenderer(screen, -1, SDL_RENDERER_ACCELERATED);
if (screen == nullptr) {
return 1;
}
init();
bool running = true;
while (running) {
SDL_Event event;
while (SDL_PollEvent(&event)) {
running &= (event.type != SDL_QUIT);
}
SDL_RenderPresent(renderer);
render();
}
SDL_DestroyWindow(screen);
SDL_Quit();
return 0;
}
When I actually run the code I do get a black screen, but the debugger lands on the line
plot(x, y, rgbmul(col, fxmul(br, ddist)));
in ; static void render(void)
This is all just "for fun" so any information or guidance is appreciated.
You define screen twice (the first time as a global variable, the second time within your main), but you initialize it only once (within your main).
Because of that, the global variable screen actually is set to nullptr and plot fails trying to use it, as the error message states.