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Fixed bug 2158 - Pixel missing in SDL_RenderDrawLines

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Sean McKean

I am running Ubuntu 12.04 (GL version 1.4 Mesa 8.0.4) , and on drawing a set of lines through the renderer through SDL_RenderDrawLines() (looped or not) or SDL_RenderDrawRect() I notice a pixel missing. For RenderDrawLines() it seems to be the second point in the sequence; for RenderDrawRect() it is the lower-right. This can be fixed by specifying SDL_RenderDrawPoint(s), but wouldn't it be easier to specify each pixel in a GL_POINTS glBegin/End loop in the OpenGL code, just to make sure?

I also ran the same program on Android; the rendering seemed to be correct, which uses glDrawArrays.
This commit is contained in:
Sam Lantinga 2013-10-20 10:10:14 -07:00
parent d914072403
commit 2a5e664b39
2 changed files with 18 additions and 51 deletions
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61
src/render/opengl/SDL_render_gl.c
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@ -1066,61 +1066,28 @@ GL_RenderDrawLines(SDL_Renderer * renderer, const SDL_FPoint * points,
int count)
{
GL_RenderData *data = (GL_RenderData *) renderer->driverdata;
int i;
GL_SetDrawingState(renderer);
data->glTranslatef(0.5f, 0.5f, 0.0f);
data->glVertexPointer(2, GL_FLOAT, 0, points);
data->glEnableClientState(GL_VERTEX_ARRAY);
if (count > 2 &&
points[0].x == points[count-1].x && points[0].y == points[count-1].y) {
data->glBegin(GL_LINE_LOOP);
/* GL_LINE_LOOP takes care of the final segment */
--count;
for (i = 0; i < count; ++i) {
data->glVertex2f(0.5f + points[i].x, 0.5f + points[i].y);
}
data->glEnd();
data->glDrawArrays(GL_LINE_LOOP, 0, count-1);
} else {
#if defined(__APPLE__) || defined(__WIN32__)
#else
int x1, y1, x2, y2;
#endif
data->glBegin(GL_LINE_STRIP);
for (i = 0; i < count; ++i) {
data->glVertex2f(0.5f + points[i].x, 0.5f + points[i].y);
}
data->glEnd();
/* The line is half open, so we need one more point to complete it.
* http://www.opengl.org/documentation/specs/version1.1/glspec1.1/node47.html
* If we have to, we can use vertical line and horizontal line textures
* for vertical and horizontal lines, and then create custom textures
* for diagonal lines and software render those. It's terrible, but at
* least it would be pixel perfect.
*/
data->glBegin(GL_POINTS);
#if defined(__APPLE__) || defined(__WIN32__)
/* Mac OS X and Windows seem to always leave the second point open */
data->glVertex2f(0.5f + points[count-1].x, 0.5f + points[count-1].y);
#else
/* Linux seems to leave the right-most or bottom-most point open */
x1 = points[0].x;
y1 = points[0].y;
x2 = points[count-1].x;
y2 = points[count-1].y;
if (x1 > x2) {
data->glVertex2f(0.5f + x1, 0.5f + y1);
} else if (x2 > x1) {
data->glVertex2f(0.5f + x2, 0.5f + y2);
} else if (y1 > y2) {
data->glVertex2f(0.5f + x1, 0.5f + y1);
} else if (y2 > y1) {
data->glVertex2f(0.5f + x2, 0.5f + y2);
}
#endif
data->glEnd();
data->glDrawArrays(GL_LINE_STRIP, 0, count);
}
/* Make sure all the line endpoints are closed.
* http://www.opengl.org/documentation/specs/version1.1/glspec1.1/node47.html
* Which points need to be drawn varies by driver, so just draw all of them.
*/
data->glDrawArrays(GL_POINTS, 0, count);
data->glDisableClientState(GL_VERTEX_ARRAY);
data->glTranslatef(-0.5f, -0.5f, 0.0f);
return GL_CheckError("", renderer);
}