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opengl: Make diagonal lines match the software renderer.

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OpenGL leaves the final line segment open, SDL's software renderer does not,
so we need a tiny bit of trigonometry here to move one more pixel in the right
direction.
This commit is contained in:
Ryan C. Gordon 2020-11-08 20:57:17 -05:00
parent da49f79500
commit 0e4ce84801
3 changed files with 24 additions and 27 deletions
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17
src/render/opengl/SDL_render_gl.c
View file

@ -865,15 +865,8 @@ GL_QueueDrawLines(SDL_Renderer * renderer, SDL_RenderCommand *cmd, const SDL_FPo
*(verts++) = 0.5f + points[i].y;
}
/* If the line segment is completely horizontal or vertical,
make it one pixel longer, to satisfy the diamond-exit rule.
We should probably do this for diagonal lines too, but we'd have to
do some trigonometry to figure out the correct pixel and generally
when we have problems with pixel perfection, it's for straight lines
that are missing a pixel that frames something and not arbitrary
angles. Maybe !!! FIXME for later, though. */
/* update the last line. */
/* Make the last line segment one pixel longer, to satisfy the
diamond-exit rule. */
verts -= 4;
{
const GLfloat xstart = verts[0];
@ -885,6 +878,12 @@ GL_QueueDrawLines(SDL_Renderer * renderer, SDL_RenderCommand *cmd, const SDL_FPo
verts[2] += (xend > xstart) ? 1.0f : -1.0f;
} else if (xstart == xend) { /* vertical line */
verts[3] += (yend > ystart) ? 1.0f : -1.0f;
} else { /* bump a pixel in the direction we are moving in. */
const GLfloat deltax = xend - xstart;
const GLfloat deltay = yend - ystart;
const GLfloat angle = SDL_atan2f(deltay, deltax);
verts[2] += SDL_cosf(angle);
verts[3] += SDL_sinf(angle);
}
}

17
src/render/opengles/SDL_render_gles.c
View file

@ -578,15 +578,8 @@ GLES_QueueDrawLines(SDL_Renderer * renderer, SDL_RenderCommand *cmd, const SDL_F
*(verts++) = 0.5f + points[i].y;
}
/* If the line segment is completely horizontal or vertical,
make it one pixel longer, to satisfy the diamond-exit rule.
We should probably do this for diagonal lines too, but we'd have to
do some trigonometry to figure out the correct pixel and generally
when we have problems with pixel perfection, it's for straight lines
that are missing a pixel that frames something and not arbitrary
angles. Maybe !!! FIXME for later, though. */
/* update the last line. */
/* Make the last line segment one pixel longer, to satisfy the
diamond-exit rule. */
verts -= 4;
{
const GLfloat xstart = verts[0];
@ -598,6 +591,12 @@ GLES_QueueDrawLines(SDL_Renderer * renderer, SDL_RenderCommand *cmd, const SDL_F
verts[2] += (xend > xstart) ? 1.0f : -1.0f;
} else if (xstart == xend) { /* vertical line */
verts[3] += (yend > ystart) ? 1.0f : -1.0f;
} else { /* bump a pixel in the direction we are moving in. */
const GLfloat deltax = xend - xstart;
const GLfloat deltay = yend - ystart;
const GLfloat angle = SDL_atan2f(deltay, deltax);
verts[2] += SDL_cosf(angle);
verts[3] += SDL_sinf(angle);
}
}

17
src/render/opengles2/SDL_render_gles2.c
View file

@ -800,15 +800,8 @@ GLES2_QueueDrawLines(SDL_Renderer * renderer, SDL_RenderCommand *cmd, const SDL_
*(verts++) = 0.5f + points[i].y;
}
/* If the line segment is completely horizontal or vertical,
make it one pixel longer, to satisfy the diamond-exit rule.
We should probably do this for diagonal lines too, but we'd have to
do some trigonometry to figure out the correct pixel and generally
when we have problems with pixel perfection, it's for straight lines
that are missing a pixel that frames something and not arbitrary
angles. Maybe !!! FIXME for later, though. */
/* update the last line. */
/* Make the last line segment one pixel longer, to satisfy the
diamond-exit rule. */
verts -= 4;
{
const GLfloat xstart = verts[0];
@ -820,6 +813,12 @@ GLES2_QueueDrawLines(SDL_Renderer * renderer, SDL_RenderCommand *cmd, const SDL_
verts[2] += (xend > xstart) ? 1.0f : -1.0f;
} else if (xstart == xend) { /* vertical line */
verts[3] += (yend > ystart) ? 1.0f : -1.0f;
} else { /* bump a pixel in the direction we are moving in. */
const GLfloat deltax = xend - xstart;
const GLfloat deltay = yend - ystart;
const GLfloat angle = SDL_atan2f(deltay, deltax);
verts[2] += SDL_cosf(angle);
verts[3] += SDL_sinf(angle);
}
}