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glBlitFramebuffer - copy a block of pixels from the read framebuffer to the draw framebuffer
void glBlitFramebuffer(GLint srcX0, GLint srcY0, GLint srcX1, GLint srcY1, GLint dstX0, GLint dstY0, GLint dstX1, GLint dstY1, GLbitfield mask, GLenum filter);
srcX0, srcY0, srcX1, srcY1 Specify the bounds of the source rectangle within the read buffer of the read framebuffer. dstX0, dstY0, dstX1, dstY1 Specify the bounds of the destination rectangle within the write buffer of the write framebuffer. mask The bitwise OR of the flags indicating which buffers are to be copied. The allowed flags are GL_COLOR_BUFFER_BIT, GL_DEPTH_BUFFER_BIT and GL_STENCIL_BUFFER_BIT. filter Specifies the interpolation to be applied if the image is stretched. Must be GL_NEAREST or GL_LINEAR.
glBlitFramebuffer transfers a rectangle of pixel values from one region of the read framebuffer to another region in the draw framebuffer. mask is the bitwise OR of a number of values indicating which buffers are to be copied. The values are GL_COLOR_BUFFER_BIT, GL_DEPTH_BUFFER_BIT, and GL_STENCIL_BUFFER_BIT. The pixels corresponding to these buffers are copied from the source rectangle bounded by the locations (srcX0; srcY0) and (srcX1; srcY1) to the destination rectangle bounded by the locations (dstX0; dstY0) and (dstX1; dstY1). The lower bounds of the rectangle are inclusive, while the upper bounds are exclusive. The actual region taken from the read framebuffer is limited to the intersection of the source buffers being transferred, which may include the color buffer selected by the read buffer, the depth buffer, and/or the stencil buffer depending on mask. The actual region written to the draw framebuffer is limited to the intersection of the destination buffers being written, which may include multiple draw buffers, the depth buffer, and/or the stencil buffer depending on mask. Whether or not the source or destination regions are altered due to these limits, the scaling and offset applied to pixels being transferred is performed as though no such limits were present. If the sizes of the source and destination rectangles are not equal, filter specifies the interpolation method that will be applied to resize the source image , and must be GL_NEAREST or GL_LINEAR. GL_LINEAR is only a valid interpolation method for the color buffer. If filter is not GL_NEAREST and mask includes GL_DEPTH_BUFFER_BIT or GL_STENCIL_BUFFER_BIT, no data is transferred and a GL_INVALID_OPERATION error is generated. If filter is GL_LINEAR and the source rectangle would require sampling outside the bounds of the source framebuffer, values are read as if the GL_CLAMP_TO_EDGE texture wrapping mode were applied. When the color buffer is transferred, values are taken from the read buffer of the read framebuffer and written to each of the draw buffers of the draw framebuffer. If the source and destination rectangles overlap or are the same, and the read and draw buffers are the same, the result of the operation is undefined.
GL_INVALID_OPERATION is generated if mask contains any of the GL_DEPTH_BUFFER_BIT or GL_STENCIL_BUFFER_BIT and filter is not GL_NEAREST. GL_INVALID_OPERATION is generated if mask contains GL_COLOR_BUFFER_BIT and any of the following conditions hold: · The read buffer contains fixed-point or floating-point values and any draw buffer contains neither fixed-point nor floating-point values. · The read buffer contains unsigned integer values and any draw buffer does not contain unsigned integer values. · The read buffer contains signed integer values and any draw buffer does not contain signed integer values. GL_INVALID_OPERATION is generated if mask contains GL_DEPTH_BUFFER_BIT or GL_STENCIL_BUFFER_BIT and the source and destination depth and stencil formats do not match. GL_INVALID_OPERATION is generated if filter is GL_LINEAR and the read buffer contains integer data. GL_INVALID_OPERATION is generated if the value of GL_SAMPLES for the read and draw buffers is not identical. GL_INVALID_OPERATION is generated if GL_SAMPLE_BUFFERS for both read and draw buffers greater than zero and the dimensions of the source and destination rectangles is not identical. GL_INVALID_FRAMEBUFFER_OPERATION is generated if the objects bound to GL_DRAW_FRAMEBUFFER_BINDING or GL_READ_FRAMEBUFFER_BINDING are not framebuffer complete.
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