Fixed bug 2158 - Pixel missing in SDL_RenderDrawLines

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.

src/render/opengl/SDL_glfuncs.h

@@ -89,8 +89,8 @@ SDL_PROC_UNUSED(void, glDepthFunc, (GLenum func))
 SDL_PROC_UNUSED(void, glDepthMask, (GLboolean flag))
 SDL_PROC_UNUSED(void, glDepthRange, (GLclampd zNear, GLclampd zFar))
 SDL_PROC(void, glDisable, (GLenum cap))
-SDL_PROC_UNUSED(void, glDisableClientState, (GLenum array))
-SDL_PROC_UNUSED(void, glDrawArrays, (GLenum mode, GLint first, GLsizei count))
+SDL_PROC(void, glDisableClientState, (GLenum array))
+SDL_PROC(void, glDrawArrays, (GLenum mode, GLint first, GLsizei count))
 SDL_PROC_UNUSED(void, glDrawBuffer, (GLenum mode))
 SDL_PROC_UNUSED(void, glDrawElements,
                 (GLenum mode, GLsizei count, GLenum type,
@@ -103,7 +103,7 @@ SDL_PROC_UNUSED(void, glEdgeFlagPointer,
                 (GLsizei stride, const GLvoid * pointer))
 SDL_PROC_UNUSED(void, glEdgeFlagv, (const GLboolean * flag))
 SDL_PROC(void, glEnable, (GLenum cap))
-SDL_PROC_UNUSED(void, glEnableClientState, (GLenum array))
+SDL_PROC(void, glEnableClientState, (GLenum array))
 SDL_PROC(void, glEnd, (void))
 SDL_PROC_UNUSED(void, glEndList, (void))
 SDL_PROC_UNUSED(void, glEvalCoord1d, (GLdouble u))
@@ -448,7 +448,7 @@ SDL_PROC_UNUSED(void, glVertex4iv, (const GLint * v))
 SDL_PROC_UNUSED(void, glVertex4s,
                 (GLshort x, GLshort y, GLshort z, GLshort w))
 SDL_PROC_UNUSED(void, glVertex4sv, (const GLshort * v))
-SDL_PROC_UNUSED(void, glVertexPointer,
+SDL_PROC(void, glVertexPointer,
                 (GLint size, GLenum type, GLsizei stride,
                  const GLvoid * pointer))
 SDL_PROC(void, glViewport, (GLint x, GLint y, GLsizei width, GLsizei height))

src/render/opengl/SDL_render_gl.c

@@ -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);
 }