this will clean all
void surface_clean(Mpaint *mpaint)
{
mpaint->surface=cairo_image_surface_create_from_png ("cxl.cache.png");
}
I want to clean the area in a cairo_surface_t by x, y, width, height.
is there any Interface?
Check CAIRO_OPERATOR_* here [1]. pycairo code:
ctx.set_source_rgba(0.0, 0.0, 0.0, 0.0)
ctx.set_operator(cairo.OPERATOR_CLEAR)
ctx.rectangle(x, y, width, height)
ctx.paint_with_alpha(1.0)
[1] https://cairographics.org/operators/
Related
In Qt Quick project, I derived a custom class from QQuickPaintedItem and mapped screen coordinate system to Cartesian coordinate system by providing a transform matrix, now I want to display a png on the custom class with QPainter->drawImage, however, the y coordinate of the image is inversed, how to fix it, thanks!
Below is the code snippet:
void DrawArea::paint(QPainter *painter)
{
painter->setRenderHint(QPainter::Antialiasing, true);
QTransform transform;
transform.setMatrix(800.0/10.0, 0.0, 0.0,
0.0, -600.0/10.0, 0.0,
400, 300, 1.0);
painter->setWorldTransform(transform);
painter->drawImage(QRectF(0, 0, 3, 3), m_image, QRectF(0, 0, m_image.width(),
m_image.height()));
}
the window size is 800x600, the Cartesian coordinate is from -5 to 5 with both x and y.
The y coord is inversed due to -600.0/10.0, but if I remove the minus sign as 600.0/10.0, the image is correct displayed, but the image extend below y=0 axis in Cartesian coordinate system.
I have a grey image. I want to draw it using a color but with opacity to a canvas. By using Color Filter, I was able to draw it on the canvas by replacing the color. If I adjust the alpha value, it changes image opacity (partial grey/red). The following code snippet shows how to draw a grey image as red onto a canvas. But how can I draw the red image as transparent to the canvas?
static void drawBrushDetail(Canvas canvas, double cx, double cy, double brushSize, double imageAngleRad) {
canvas.translate(cx + brushSize / 2, cy + brushSize / 2);
ui.Image bt = imgBrushTip; //this is a gray image
Color selectedColor = getDrawColor(cx,cy);
final _paint = Paint();
var alphaVal=255;
//if I change alphaVal to 100, the final draw looks more gray instead of red with 100 Alpha
_paint.colorFilter = ColorFilter.mode(selectedColor.withAlpha(alphaVal), BlendMode.srcATop);
if (imageAngleRad != 0.0) canvas.rotate(imageAngleRad);
canvas.translate(-brushSize / 2, -brushSize / 2);
// draw image with specified brushSize
canvas.drawImageRect(bx, Rect.fromLTRB(0, 0, bt.width, bt.height),
Rect.fromLTRB(0, 0, brushSize, brushSize), _paint);
//traslate back, don't want to use save and restore layer since it's expensive
canvas.translate(brushSize / 2, brushSize / 2);
if (imageAngleRad != 0.0) canvas.rotate(-imageAngleRad);
canvas.translate(-cx - brushSize / 2, -cy - brushSize / 2);
}
See the image below. The above code will paint the image with solid red color. (image pointed by the red arrow). But I want the result to be an image with red color and transparent. Since in Flutter, there is no API to set alpha for canvas, don't know if it is possible.
I figured it out but the credit goes to pskink
I only need to draw one image(gray color) but I need to do the followings:
Resize and rotate the image.
Replace the gray image with red color.
Draw the image (now in red) with opacity.
Here is the code snippet.
static void drawBrushDetail1(Canvas canvas, double cx, double cy, double size) {
final _paint = Paint();
const opacity = 0.5;
_paint.color = Color.fromRGBO(0, 0, 0, opacity);
ui.Image bx = uiImg[0];
double scale = size / 60; //size is brush tip size and 60x60 is gray image size
canvas.drawAtlas(
bx,
[
RSTransform.fromComponents(
rotation: imageAngleRad,
scale: scale,
anchorX: 30,
anchorY: 30,
translateX: cx,
translateY: cy)
],
[
/* The size of gray image is 60 x 60 */
const Rect.fromLTWH(0, 0, 60, 60)
],
[Colors.red],
BlendMode.dstIn, /*This is replace the gray image wiht red color
null /* No need for cullRect */,
_paint); //_paint will paint the red image in 0.5 opacity
}
width, height = max(abs(fromo.realx - to.realx),3), max(abs(fromo.realy - to.realy),3)
surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
ctx = cairo.Context(surface)
ctx.scale(width, height)
ctx.move_to(0, 0)
ctx.line_to(1, 1)
I have that, i want to convert the cairo context to a pixbuf so i can use it as Gtk.Image. Can I do that?
You can use gtk_image_set_from_surface for that:
gtk.Image.set_from_surface(surface)
or even make your image from the surface:
gtk.Image.new_from_surface(surface)
I'm trying to figure out what all these arguments do, as when I draw my bullet image it appears as a solid block instead of a sprite that alternates between solid color and an empty portion (i.e instead of 10101 it's 11111, with 0's being empty parts in the texture).
Before, I was using batch.draw(texture, float x, float y) and it displays the texture correctly. However I was playing around with rotation, and this is the version of draw that seemed most suitable:
batch.draw(texture, x, y, originX, originY, width, height, scaleX, scaleY, rotation, srcX, srcY, srcWidth, srcHeight, flipX, flipY)
I can figure out the obvious ones, those being originX, originY (location to draw the image from its upper left pixel I believe) however then I don't know what the x, y coordinate after texture is for.
scaleX,scaleY, rotation, and flipX, flipY I know what to do with, but what is srcX and srcY, along with the srcWidth and srcHeight for?
edit: I played around and figured out what the srcX,srcY and srcHeight,Width do. I can not figure out what originX,Y does, even though I'm guess it's the centerpoint of the image. Since I don't want to play around with this one anyway, should I leave it as 0,0?
What would be common uses for manipulating the centerpoint of images?
Answering main question.
srcX, srcY, srcWidth, srcHeight are values determine which part (rectangle) of source texture you want to draw. For example, your source image is 100x100 pixels of size. And you want to draw only 60x60 part in a middle of source image.
batch.draw(texture, x, y, 20, 20, 60, 60);
Answering your edited question.
Origin is a center point for rotation and scale transformations. So if you want to your sprite scales and rotates around it's center point you should set origin values so:
float originX = width * 0.5f;
float originY = height * 0.5f;
In case you don't care about rotation and scaling you may not specify this params (leave it 0).
And keep in mind, that origin is not determines image drawing position (this is most common mistake). It means that two next method calls are draw image at same position (forth and fifth params are originX and originY):
batch.draw(image, x, y, 0, 0, width, height, ...);
batch.draw(image, x, y, 50, 50, width, height, ...);
According to the documentation, the parameters are as defined:
srcX - the x-coordinate in texel space
srcY - the y-coordinate in texel space
srcWidth - the source with in texels
srcHeight - the source height in texels
So I'm starting to work with openGL, been following the tutorials over at Jeff LaMarche's blog and I've run into a problem when trying to draw a square using the GL_TRIANGLE_STRIP mode with glDrawArrays.
It works, by that I mean that I can draw a square, but I get this weird drawing glitch. You can see it here:
Drawing glitch http://img10.imageshack.us/img10/1631/picture1io.png
I'm using the xcode template that's provided by Jeff, so I assume the setup is all proper. The code I'm using in the drawView function is as follows:
Square2D *square = malloc(sizeof(Square2D));
Square2DSet(square, -0.25, -0.25, -20.0, 0.5, 0.5);
glLoadIdentity();
glClearColor(0.7, 0.7, 0.7, 1.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnableClientState(GL_VERTEX_ARRAY);
glColor4f(1.0, 0.0, 0.0, 1.0);
glVertexPointer(3, GL_FLOAT, 0, square);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 12);
glDisableClientState(GL_VERTEX_ARRAY);
if(square != NULL)
free(square);
here's the code for Square2d and Square2DSet:
typedef struct {
Vertex3D tl;
Vertex3D bl;
Vertex3D tr;
Vertex3D br;
} Square2D;
static inline void Square2DSet(Square2D *sq, GLfloat x, GLfloat y, GLfloat z, GLfloat width, GLfloat height)
{
sq->tl = Vertex3DMake(x, y, z);
sq->bl = Vertex3DMake(x, y + height, z);
sq->tr = Vertex3DMake(x + width, y, z);
sq->br = Vertex3DMake(x + width, y + height, z);
}
I'm sure I'm doing something wrong, just not sure what. Eventually the glitch will go away after the program has run for a little bit.
Any ideas?
Cheers
glDrawArrays(GL_TRIANGLE_STRIP, 0, 12);
is drawing 12 vertices. You want 4. Its asking how many indices, not how many values to look at. It will multiply the index by the number of values at each index.
The reason why its going crazy is because its drawing junk, then it disappears because I assume that junk gets filled with 0s or something and it just goes away.