[英]OpenGL — Multiple glDrawArrays() calls only showing results from first?
[英]opengl not showing output from renderFunction
我正在使用opengl實現此dda算法。 但是,由於某種原因,它不會繪制第二行。 我嘗試將printf放在每一行,這表明它正在執行。 但是,我的窗口中沒有輸出
#include <GL/gl.h>
#include <GL/glut.h>
#include <stdio.h>
int choice = 0;
void DDA(x0, y0, x1, y1)
const x0, y0, x1, y1;
{
glOrtho(-500, 500, -500, 500, -1, 1);
float dx = x1 - x0;
float dy = y1 - y0;
int steps = abs(dx) > abs(dy) ? abs(dx) : abs(dy);
float xInc = (float)steps/dx;
float yInc = (float)steps/dy;
int x = x0, y = y0;
for(int i = 0; i < steps; i++) {
glBegin(GL_POINTS);
glColor3f(1.0, 3.0, 2.0);
glVertex2i(x, y);
x += xInc;
y += yInc;
glEnd();
glFlush();
}
}
void Bresenham(x0, y0, x1, y1)
const x0, y0, x1, y1;
{
glOrtho(-500, 500, -500, 500, -1, 1);
int x = x0;
int y = y0;
int dx = x1 - x0;
int dy = y1 - y0;
int p = 2*dy-dx;
int m = dy / dx;
glBegin(GL_POINTS); {
glColor3f(2.0, 3.0, 5.0);
while(x != x1) {
if(m < 1) {
glVertex2i(x, y);
x++;
if(p >= 0) {
p += 2*(dy - dx);
y++;
}
else {
p += 2*dy;
}
}
else {
glVertex2i(x, y);
y++;
if(p >= 0) {
p += 2*(dx - dy);
x++;
}
else {
p += 2*dx;
}
}
}
glVertex2i(x, y);
}
glEnd();
glFlush();
}
void circle(x0, y0, r)
const x0, y0, r;
{
}
void renderDDA(void) {
DDA(0, 0, 300, 400);
DDA(0, 0, 200, 200);
}
void renderBresenham(void) {
Bresenham(0, 0, 300, 100);
Bresenham(0, 0, 500, 0);
}
void renderCircle(void) {
}
main(argc, argv)
char** argv;
{
redo:
printf("ENTER YOUR CHOICE: ");
scanf("%d", &choice);
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
glutInitWindowPosition(0, 0);
glutInitWindowSize(1920, 1680);
glutCreateWindow(argv[1]);
glClear(GL_COLOR_BUFFER_BIT);
glClearColor(0.0, 0.0, 0.0, 0.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
switch (choice) {
case 0:
glutDisplayFunc(renderDDA);
break;
case 1:
glutDisplayFunc(renderBresenham);
break;
case 2:
glutDisplayFunc(renderCircle);
break;
default:
printf("NO SUCH CHOICE!!");
goto redo;
}
glutMainLoop();
return 0;
}
我也嘗試過換線。 然后,它僅繪制上線。 它確實執行第二次調用。
glOrtho
不設置正交投影,它定義了正交投影矩陣並將當前矩陣乘以正交投影矩陣。
您必須在調用glOrtho
之前設置單位矩陣:
glLoadIdentity();
glOrtho(-500, 500, -500, 500, -1, 1);
此外,算法中存在問題。 x
和y
的類型必須為float
。 如果將結果截斷為int
,則只能繪制與45度的倍數對齊的角度的線,因為x
和y
在每一步都精確地由0或1改變:
float x = x0, y = y0;
for(int i = 0; i < steps; i++) {
glBegin(GL_POINTS);
glColor3f(1.0, 3.0, 2.0);
glVertex2i((int)(x+0.5f), (int)(y+0.5f));
x += xInc;
y += yInc;
glEnd();
}
注意,將類型從int
更改為float
會導致對x
和y
進行全精度跟蹤。 glVertex2i((int)(x+0.5f), (int)(y+0.5f))
確保繪制點時將坐標( x
, y
)舍入到整數位置。
我建議投影矩陣的設定從並移動glFlush
從DDA
分別Bresenham
到renderDDA
分別renderBresenham
:
void DDA(float x0, float y0, float x1, float y1)
{
float dx = x1 - x0;
float dy = y1 - y0;
int steps = abs(dx) > abs(dy) ? abs(dx) : abs(dy);
float xInc = (float)steps/dx;
float yInc = (float)steps/dy;
float x = x0, y = y0;
for(int i = 0; i < steps; i++) {
glBegin(GL_POINTS);
glColor3f(1.0, 3.0, 2.0);
glVertex2i((int)(x+0.5f), (int)(y+0.5f));
x += xInc;
y += yInc;
glEnd();
}
}
void Bresenham(float x0, float y0, float x1, float y1)
{
int x = x0;
int y = y0;
int dx = x1 - x0;
int dy = y1 - y0;
int p = 2*dy-dx;
int m = dy / dx;
glBegin(GL_POINTS); {
glColor3f(2.0, 3.0, 5.0);
while(x != x1) {
if(m < 1) {
glVertex2i(x, y);
x++;
if(p >= 0) {
p += 2*(dy - dx);
y++;
}
else {
p += 2*dy;
}
}
else {
glVertex2i(x, y);
y++;
if(p >= 0) {
p += 2*(dx - dy);
x++;
}
else {
p += 2*dx;
}
}
}
glVertex2i(x, y);
}
glEnd();
}
void renderDDA(void) {
glLoadIdentity();
glOrtho(-500, 500, -500, 500, -1, 1);
DDA(0, 0, 300, 400);
DDA(0, 0, 200, 200);
glFlush();
glutSwapBuffers();
}
void renderBresenham(void) {
glLoadIdentity();
glOrtho(-500, 500, -500, 500, -1, 1);
Bresenham(0, 0, 300, 100);
Bresenham(0, 0, 500, 0);
glFlush();
glutSwapBuffers();
}
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