我想在SDL中绘制一个多边形。边数将由程序在运行时确定。任何人都可以帮我解决这个问题吗？
答案 0 :(得分：3)
它不是原生SDL，但有一个库sdl_gfx，它具有filledPolygonColour功能。
答案 1 :(得分：0)
几年前我有同样的问题我found the following implementation：
bool DrawFilledPolygon(PolygonShape poly, const SDL_Color color, SDL_Renderer* renderer) {
int topY; // used to hold the y coordinate of the top vertex
int topCnt; // used to hold the index of the top vertex
int leftCnt; // used to hold the index of the vertex left of the top vertex
int rightCnt; // used to hold the index of the vertex right of the top vertex
int startX; // Starting point to draw the line, uses FP math
int endX; // ending point to draw the line, uses FP math
int cntY; // y position of the current line
int leftSlope; // Slope of the left side, uses FP math
int rightSlope; // Slope of the right side, uses FP math
int cnt; // counting variable used in loops
int numVerts = poly.GetNumberOfVertices(); // number of vertices in the polygon being drawn, initialize immediately
int numVertsProc = 1; // number of vertices that have been processed, initialize to 1
Point center = poly.GetCenter();
Point *verts = poly.GetVertices(); // Vertex information of the polygon
topY = verts[0].y; // Initialize the top y coordinate to the first point
topCnt = 0; // set to top point to 0
// assumes points in counterclockwise order
// find the true top point
for(cnt = 1; cnt < numVerts; cnt++) // for all the vertices in the polygon
{
if(verts[cnt].y < topY) // if vertex of the current vertex is above the top vertex
{
topY = verts[cnt].y; // set the top vertex to the current vertex
topCnt = cnt; // set the reference number of the top vertex
}
}
// find point to left
leftCnt = topCnt - 1; // set the left point to one less than the top point
if(leftCnt < 0) // if the left vertex specified is less than 0
leftCnt = numVerts - 1; // set the left vertex to the top vertex
// find point to right
rightCnt = topCnt + 1; // set the right vertex to one more than the top vertex
if(rightCnt >= numVerts) // if the right vertex specified is more than the number of vertices
rightCnt = 0; // set it equal to 0
startX = endX = (verts[topCnt].x + center.x) << 16; // set the starting and ending points of the line
cntY = verts[topCnt].y; // set the first y value to draw at
if(verts[leftCnt].y != verts[topCnt].y) // if the top and left vertex do not have the same y value
leftSlope = ((verts[leftCnt].x - verts[topCnt].x) << 16) / (verts[leftCnt].y - verts[topCnt].y); // find the left side slope
if(verts[rightCnt].y != verts[topCnt].y) // if the top and right vertex do not have the same y value
rightSlope = ((verts[rightCnt].x - verts[topCnt].x) << 16) / (verts[rightCnt].y - verts[topCnt].y); // find the right side slope
SDL_SetRenderDrawColor(renderer, color.r, color.g, color.b, color.a);
// find slopes
while(numVertsProc < numVerts) // if there remain vertices to be processed
{
// rasterize to first point
while(cntY < verts[leftCnt].y && cntY < verts[rightCnt].y) // while one of the two side points hasn't been reached yet
{
SDL_RenderDrawLine(renderer, startX >> 16, cntY + center.y, endX >> 16, cntY + center.y);
//DrawLine(Point(startX >> 16, cntY + center.y), Point(endX >> 16, cntY + center.y), col); // draw a line between the sides
cntY++; // increment the y position by 1
startX += leftSlope; // increase the starting x value by the left slope
endX += rightSlope; // increase the ending x value by the right slope
}
// set top point to point met
// set point met to next point
// find new slope
if(verts[leftCnt].y <= cntY) // if the raster line passes the left coordinate
{
topCnt = leftCnt; // set the top point to the left side
leftCnt--; // decrement the left point
if(leftCnt < 0) // if the left point is less than zero
leftCnt = numVerts - 1; // wrap around
if(verts[leftCnt].y != verts[topCnt].y) // if the top and new left vertex do not have the same y value
leftSlope = ((verts[leftCnt].x - verts[topCnt].x) << 16) / (verts[leftCnt].y - verts[topCnt].y); // find the left side slope
startX = (verts[topCnt].x + center.x) << 16; // set the starting x position
numVertsProc++; // increment the number of vertices processed
}
if(verts[rightCnt].y <= cntY) // if the raster line passes the right coordinate
{
topCnt = rightCnt; // set the top point to the right side
rightCnt++; // increment the right point
if(rightCnt == numVerts) // if the right point is more than the number of vertices
rightCnt = 0; // set the right point to zero
if(verts[rightCnt].y != verts[topCnt].y) // if the top and new right vertex do not have the same y value
rightSlope = ((verts[rightCnt].x - verts[topCnt].x) << 16) / (verts[rightCnt].y - verts[topCnt].y); // find the right side slope
endX = (verts[topCnt].x + center.x) << 16; // set the ending x position
numVertsProc++; // increment the number of vertices processed
}
SDL_RenderDrawLine(renderer, startX >> 16, cntY + center.y, endX >> 16, cntY + center.y);
//DrawLine(Point(startX >> 16, cntY + center.y), Point(endX >> 16, cntY + center.y), col); // draw a line between the sides
}
// continue until the number of vertices p0 has touched == number of vertices
return true; // return success
}
通过这段代码我改编了我的代码，以便按如下方式进行测试：
#include "SDL.h"
//#include "SDL_image.h"
//#include "SDL_ttf.h"
//#include "SDL_mixer.h"
#include <iostream>
#include <vector>
class Point {
public:
Point() {};
Point(int x, int y) { this->x = x; this->y = y; };
int x, y;
};
class PolygonShape {
public:
PolygonShape(std::vector<Point> vertices);
~PolygonShape();
Point GetCenter(void);
Point * GetVertices(void);
int GetNumberOfVertices(void);
private:
Point * vertices;
Point center;
int length;
};
PolygonShape::PolygonShape(std::vector<Point> vertices){
int minX = 0xFFFF, minY = 0xFFFF, maxX = 0, maxY = 0;
this->length = vertices.size();
this->vertices = new Point[length];
for (int i = 0; i < this->length; i++) {
this->vertices[i] = Point(vertices[i].x, vertices[i].y);
if (this->vertices[i].x > maxX) maxX = this->vertices[i].x;
if (this->vertices[i].x < minX) minX = this->vertices[i].x;
if (this->vertices[i].y > maxY) maxY = this->vertices[i].y;
if (this->vertices[i].y < minY) minY = this->vertices[i].y;
}
this->center.x = minX + ((maxX - minX) / 2);
this->center.y = minY + ((maxY - minY) / 2);
}
PolygonShape::~PolygonShape() {
delete[] this->vertices;
}
Point PolygonShape::GetCenter(void) {
return center;
}
Point * PolygonShape::GetVertices(void) {
return this->vertices;
}
int PolygonShape::GetNumberOfVertices(void) {
return this->length;
}
主要功能：
int main(int argc, char** argv) {
if (SDL_Init(SDL_INIT_EVERYTHING) != 0) {
std::cout << "SDL_Init Error: " << SDL_GetError() << std::endl;
return 1;
}
SDL_Window *win = SDL_CreateWindow("Prueba", 100, 100, 960, 540, SDL_WINDOW_SHOWN);
if (win == NULL) {
std::cout << "SDL_CreateWindow Error: " << SDL_GetError() << std::endl;
return 1;
}
SDL_Renderer *ren = SDL_CreateRenderer(win, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
if (ren == NULL) {
std::cout << "SDL_CreateRenderer Error: " << SDL_GetError() << std::endl;
return 1;
}
SDL_RenderClear(ren);
SDL_Color color = {.r = 255, .g = 255, .b = 255, .a = 255 };
std::vector<Point> vertices;
vertices.push_back(Point(10, 10));
vertices.push_back(Point(100, 10));
vertices.push_back(Point(150, 75));
vertices.push_back(Point(20, 105));
PolygonShape poly = PolygonShape(vertices);
DrawFilledPolygon(poly, color, ren);
SDL_RenderPresent(ren);
getchar();
SDL_DestroyRenderer(ren);
SDL_DestroyWindow(win);
SDL_Quit();
return 0;
}
我希望它可以帮到你！ ： - ）