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Added line drawing using Bresenham's line algorithm (thanks @rtrussell!)

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This commit is contained in:
Sam Lantinga 2022-01-08 10:59:31 -08:00
parent fe3a33a092
commit 9f56faeedc
1 changed files with 123 additions and 8 deletions
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131
src/render/SDL_render.c
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@ -2782,13 +2782,129 @@ SDL_RenderDrawLineF(SDL_Renderer * renderer, float x1, float y1, float x2, float
return SDL_RenderDrawLinesF(renderer, points, 2);
}
static int plotLineLow(SDL_Renderer *renderer, float x0, float y0, float x1, float y1)
{
int retval = 0;
float dx = x1 - x0;
float dy = y1 - y0;
int yi = 1;
float x, y, D;
int count = (x1 - x0 + 1);
SDL_bool isstack;
SDL_FPoint *points = SDL_small_alloc(SDL_FPoint, count, &isstack);
SDL_FPoint *tmp = points;
if (dy < 0) {
yi = -1;
dy = -dy;
}
D = (2 * dy) - dx;
y = y0;
for (x = x0; x <= x1; ++x) {
tmp->x = x;
tmp->y = y;
tmp++;
if (D > 0) {
y += yi;
D += 2 * (dy - dx);
} else {
D += 2*dy;
}
}
if (renderer->scale.x != 1.0f || renderer->scale.y != 1.0f) {
retval = RenderDrawPointsWithRectsF(renderer, points, count);
} else {
retval = QueueCmdDrawPoints(renderer, points, count);
}
SDL_small_free(points, isstack);
return retval;
}
static int plotLineHigh(SDL_Renderer *renderer, float x0, float y0, float x1, float y1)
{
int retval = 0;
float dx = x1 - x0;
float dy = y1 - y0;
int xi = 1;
float x, y, D;
int count = (y1 - y0 + 1);
SDL_bool isstack;
SDL_FPoint *points = SDL_small_alloc(SDL_FPoint, count, &isstack);
SDL_FPoint *tmp = points;
if (dx < 0) {
xi = -1;
dx = -dx;
}
D = (2 * dx) - dy;
x = x0;
for (y = y0; y <= y1; ++y) {
tmp->x = x;
tmp->y = y;
tmp++;
if (D > 0) {
x += xi;
D += 2 * (dx - dy);
} else {
D += 2*dx;
}
}
if (renderer->scale.x != 1.0f || renderer->scale.y != 1.0f) {
retval = RenderDrawPointsWithRectsF(renderer, points, count);
} else {
retval = QueueCmdDrawPoints(renderer, points, count);
}
SDL_small_free(points, isstack);
return retval;
}
static int plotLineBresenham(SDL_Renderer *renderer, float x0, float y0, float x1, float y1)
{
if (SDL_fabs(y1 - y0) < SDL_fabs(x1 - x0)) {
if (x0 > x1) {
return plotLineLow(renderer, x1, y1, x0, y0);
} else {
return plotLineLow(renderer, x0, y0, x1, y1);
}
} else {
if (y0 > y1) {
return plotLineHigh(renderer, x1, y1, x0, y0);
} else {
return plotLineHigh(renderer, x0, y0, x1, y1);
}
}
}
static int
RenderDrawLinesWithPointsF(SDL_Renderer * renderer,
const SDL_FPoint * points, const int count)
{
int i;
int retval = 0;
for (i = 0; i < count-1; ++i, ++points) {
retval += plotLineBresenham(renderer, points[0].x, points[0].y, points[1].x, points[1].y);
}
if (retval < 0) {
retval = -1;
}
return retval;
}
static int
RenderDrawLinesWithRectsF(SDL_Renderer * renderer,
const SDL_FPoint * points, const int count)
{
SDL_FRect *frect;
SDL_FRect *frects;
SDL_FPoint fpoints[2];
int i, nrects = 0;
int retval = 0;
SDL_bool isstack;
@ -2818,12 +2934,7 @@ RenderDrawLinesWithRectsF(SDL_Renderer * renderer,
frect->w = (maxX - minX + 1) * renderer->scale.x;
frect->h = renderer->scale.y;
} else {
/* FIXME: We can't use a rect for this line... */
fpoints[0].x = points[i].x * renderer->scale.x;
fpoints[0].y = points[i].y * renderer->scale.y;
fpoints[1].x = points[i+1].x * renderer->scale.x;
fpoints[1].y = points[i+1].y * renderer->scale.y;
retval += QueueCmdDrawLines(renderer, fpoints, 2);
retval += RenderDrawLinesWithPointsF(renderer, &points[i], 2);
}
}
@ -2886,6 +2997,7 @@ SDL_RenderDrawLinesF(SDL_Renderer * renderer,
const SDL_FPoint * points, int count)
{
int retval = 0;
int use_renderpoints;
int use_rendergeometry;
CHECK_RENDERER_MAGIC(renderer, -1);
@ -2904,9 +3016,12 @@ SDL_RenderDrawLinesF(SDL_Renderer * renderer,
}
#endif
use_renderpoints = 1;
use_rendergeometry = 1;
if (use_rendergeometry) {
if (use_renderpoints) {
retval = RenderDrawLinesWithPointsF(renderer, points, count);
} else if (use_rendergeometry) {
SDL_bool isstack1;
SDL_bool isstack2;
const float scale_x = renderer->scale.x;